Why can't element with paired electron have colour

I know that elements with unpaired electrons are coloured especially the d-block element which can be explained by crystal field theory. But, why can't element with paired electrons give colour, is it because the energy gap is too large ?

• It's not about whether the electrons are paired or not. It has to do with whether the electronic transitions in the molecule lie within the visible spectrum – orthocresol Sep 30 '15 at 15:20
• to give you counterexamples, Ni(II) in its dimethylglyoxime complex has 8 d electrons and all of them are paired but the complex is red. On the other hand $\ce{O2}$ gas has 2 unpaired electrons but it's colourless. – orthocresol Sep 30 '15 at 15:30
• @orthocresol actually, liquid oxygen has a blueish colour, or so I heard. – Jan Sep 30 '15 at 16:36
• @Jan I've seen that before in a demonstration... which is why I said O2 gas :D Anyway I went to read up. Turns out that the blue colour is because of two O2 molecules being excited simultaneously, which has a very low probability of occurring in the gas phase (hence colourless). Probably wasn't the best example to use but I guess it's passable. – orthocresol Sep 30 '15 at 16:58
• @orthocresol Disregard me, I overread the 'gas' in there ^^' But on that note: chlorine gas is greenish, bromine is brown, iodine is purple, liquid chlorine is yellow. – Jan Sep 30 '15 at 16:59