I am working on a story for adaptation into animation. Main lead is a chemist in a traditional fantasy setting. The chemist uses her own compound to battle using fire or explosions. I love the chemistry to be grounded. I am looking for a very combustible gas or liquid that has a color. Preferably green-blueish. Preferably lighter than air. Does this exist? Any other suggestions about other cool looking compounds are very welcome.
Here is one possible embodiment for your story that is grounded in actual chemistry.
Warning dangerous explosive mixture is possible in reality, so as to mitigate potential danger, I recommend the use of only small amounts (say, a test tube) of hydrogen and chlorine gas in a well-ventilated setting.
The first step is to mix hydrogen and chlorine gas in a vessel. I would recommend for safety a deflated clear plastic bag devoid of any air/oxygen contamination.
Upon intended or accidental detonation, that can occur apparently via several paths, for example, per a reference, to quote:
The reaction of chlorine and hydrogen can be initiated by direct sunlight, other sources of ultraviolet light, static electricity, or sharp impact.
And produce primarily a shock wave with associated high temperatures and possible container shrapnel.
With all appropriate safety measures in place, expose the H2/Cl2 gas mix to a LED light consisting of UV light, or a spark. This results in a chain reaction cumulating in a very vigorous powerful explosion. Also, sunlight exposure may also result in unintended detonation in situations where there is a higher amount of reflective UV rays (as, for example, from a lake, ocean, snow,..).
Chlorine gas has some coloration against a white background. However, due to hydrogen dilution, likely less intense here, so close-up photography is likely required. Try increasing chlorine concentration to alleviate the coloration issue, as per a source, to quote:
mixture of hydrogen and chlorine is exploded by almost any form of energy (heat, sunlight, sparks etc). Explosive range: 5-95%.
Also, try dissolving the Cl2 in CCl4 (this may also help with the O2 contamination which stops the chain reaction).
See associated available videos here.
A novel last embodiment, yet to be verified (albeit, the associated chain reaction chemistry appears supportive of) is the reaction between chlorine (absence of any oxygen), hydrogen with added select metals imbued with hydrogen.
To construct the latter, for example, the insertion of Aluminum or Magnesium metal in HCl will, at least temporarily, possess an active surface presence of absorbed hydrogen (see this commentary by ScienceDirect and more extensive from De Gruyter).
As per a source already noted, various dry metal hydrides can ignite in chlorine, so this likely results in a detonation of the mixture. Additional caution should also be noted, as select metal hydrides, as powders, can even augment explosive powers.