Quote:
Originally Posted by whswhs
With green, copper would be more likely, or magnesium (which I think is the analog of iron in the chlorophyll molecule).
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That's right. Chlorophyll and haem are somewhat similar molecules, with iron giving haem its characteristic red colour, and magnesium taking the analogous place in chlorophyll, resulting in green.
Chromium compounds give a startling range of colours, partly because chromium is kind-of stable in a wide range of oxidation states. Chromium (II) is the one you would need in a close haemoglobin analog, and that tends to be not-all-that-stable-really and bright blue. The yellow pigments are mostly chromates, I think, with chromium in the (VI) oxidation state where it is chemically very unlike iron or magnesium (electron accepting rather than electron donating).
However, if you are in a world where the existence of the luminiferous aether somehow allows spaceships to take off from Earth's surface without monstrous rocketry, no-one is going to quibble much over the details of chemistry. And if they did, you could simply tell them that this chromate-rich respiratory pigment was only a functional analogue of haemoglobin, not a chemical analogue.