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Why is gold golden?

Yes, this is a beautiful question. As you said, in lower rows of the periodic table, there are relativistic effects for the electrons. That is, for core electrons in gold, the electrons are traveling ...
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131 votes

Why is gold golden?

See the footnotes I've included if you would like to see more of the detail behind a specific statement. The figure below compares the reflectance spectrum for silver and gold (let's forget about ...
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82 votes
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Is it true that heavy water is not blue?

Based on your description, I may have found the article you originally saw, or at least one very similar. Researchers from Dartmouth College published a paper$\mathrm{^1}$ in which they report, among ...
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69 votes

Is it true that heavy water is not blue?

This does seem to be the case. I don't have images of the different types of water, but I did find this overlaid IR-visible spectrum of water and heavy water: As you stated, the presence of deuterium ...
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61 votes

Why is gold golden?

This effect comes from the band structure of the metal, not atoms. In simplest terms (see, e.g., Ashcroft & Mermin, Solid State Physics, chapter 1) the electrons in the conduction band have a ...
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33 votes
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Why is snow white?

The difference between snow and ordinary ice cubes is mainly about the size of the particles. Snow is made from small, irregular crystals with many edges at a very small scale. Light is refracted or ...
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28 votes
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Does O2 have a color in the gas phase

Background $\ce{O2}$ exists as a paramagnetic, triplet since the two electrons in its two (degenerate) HOMO orbitals are unpaired. There are 6 known phases of solid oxygen with color ranging from ...
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26 votes
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Soaps come in different colors, but why is soap lather always white?

Though @DHMO's answer is quite interesting, you shouldn't take it without a pinch of salt. I've to disagree with it in some aspects. Soap colorants range from various kinds of Mica to dyes found ...
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26 votes
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What gives fresh milk a yellow tinge?

The main substances that cause the yellowish color of the milk are carotenoids [1]. The main carotene involved is the beta-carotene coming from the feed that cows eat. Some studies have been carried ...
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26 votes
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What makes ABS plastic turn yellow?

What you're specifically describing is typically known as UV degradation. The color change is due to the oxidation of the polymers that make up the plastic. These chemical reactions are demonstrated ...
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24 votes

Can flames be colored black?

This video shows how a black flame is achieved. If you illuminate the fire with a monochromatic light source (sodium vapor lamp) and introduce a species in the fire that absorbs that wavelength (...
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23 votes
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Why do transition elements make colored compounds?

You are absolutely correct, it all about the metal's electrons and also about their d orbitals. Transition elements are usually characterised by having d orbitals. Now when the metal is not bonded ...
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22 votes
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What causes the iridescent colour in laboratory grown bismuth?

The colour is from a thin film of bismuth(III) oxide that forms on the surface if the crystals are formed in air. At the elevated temperatures used to melt bismuth, the oxide forms quite quickly. The ...
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22 votes
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Why is manganese(II) coloured although the transition should be spin-forbidden?

Selection rules The intensity of the transition from a state $\mathrm{i}$ to a state $\mathrm{f}$ is governed by the transition dipole moment $\mu_{\mathrm{fi}}$ (strictly, it is proportional to $|\...
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22 votes
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What exact color does ozone gas have?

Due to Chappuis absorption, ozone does have a bluish color. To determine exactly what kind of blue it is, let's first look at the spectrum of absorption in the Chappuis band. The following plot was ...
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20 votes
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Does bleach turn a substance white or colorless?

First, let's think about what makes a substance coloured: a substance will appear to be coloured if it absorbs light in the visible spectrum. Beta carotene: absorbs blue/green light (400–500 nm), ...
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20 votes
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Are there colorful metals besides gold and copper?

Osmium has a bluish-gray tint. Well; slightly. Cesium is silvery-golden!, But don't wear it.
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20 votes
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Explanation for why nickel turns green in hydrochloric acid

The question is really badly worded. For starters, let’s look at solutions of nickel(II): Figure 1: Nickel(II) solutions. From left to right: $\ce{[Ni(NH3)6]^2+}$, $\ce{[Ni(en)3]^2+}$, $\ce{[NiCl4]^2-...
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18 votes
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What is the origin of the colour of azo dyes?

Yes, it is all about the absorption of light at specific wavelength. Azobenzene, the parent compound has an absorption maximum around $\lambda$= 430 nm in the visible spectrum. The interesting part ...
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17 votes
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Color changes of a solution of acetone and sodium hydroxide

Under basic condtions, acetone does condense with itself, first to form mesityl oxide, which is colorless, and then to form isophorone, which has a yellow color. Both mesityl oxide and isophorone are ...
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17 votes

Soaps come in different colors, but why is soap lather always white?

You might have observed that large soap bubbles are transparent. This is because the color has been diluted to a great extent that it basically became transparent. Now, the foam is just a multitude ...
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16 votes
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How can the intense color of potassium permanganate be explained with molecular orbital theory?

Let’s take a look at a qualitative MO scheme for a tetrahedric transition metal complex whose ligands have three p-type orbitals each. On the left of figure 1 you have the metal orbitals ($\mathrm{3d}$...
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16 votes
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Why/how is blood red? (colours of hemoglobin)

The $\ce{Fe}$-porphyrin complex is a vastly conjugated $\pi$-system, in which the oxidation state of the $\ce{Fe}$ plays a central role. The wavelength of light absorbed by hemoglobin exactly ...
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16 votes
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What gives milk its characteristic white color?

There is no "pigment" that makes milk white. According to Wikipedia: A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective ...
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16 votes
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Colour of platinum

In bulk metals, electrons in the conduction band are shared, creating a "sea" of reflective electrons. A nanoparticle, though, is so small that there is no conduction "band", just discrete levels ...
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14 votes
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Flame test: Is the metal atom or the metal ion responsible for the flame colour?

The phenomenon that is witnessed during a flame test is an "atomic emission". This statement may seem inappropriate, since it is a solution of metal ions (and not atoms) that is tested. The reason for ...
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14 votes
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Why is tetrathiocyanatocobaltate(II) blue?

Let us consider this qualitatively with crystal field theory (CFT). Co is a transition metal with $d^7$ configuration. CFT says that depending on the geometry of the metal complex, the d-orbital ...
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14 votes

Why are acids usually depicted in fiction as green?

The green is the color of bile which usually accompanies gastric acid. Acid in its original context referred to a bitter taste. Bitter tasting compounds, such as vinegar, is what led to the modern ...
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