Please talk more about comparative space-anatomy and biology! I am honestly interested in this stuff; and as someone who has exams soon, I know the feel. Any way you can make twi'lek stuff relevant to what you have to study?
YES oooooooo I have a whole entire deal with them, and it is color based. We see a WIDE range of Twi’lek Colors, I will focus now on White, Flesh Tones (we only see a pale “white” tone but the whole range of human pigments could be possible), Red, Orange Yellow, Green, Blue, and Purple.
Now, these colors are not all present in mammals, so I’m going to have to talk about bird/reptile systems, but we can extrapolate.
Color is formed by two methods- pigment and structural color. Within the dermis, there are several types of pigment cells. There are melanophores, responsible for black, brown, and even a ruddy red color like you might find naturally in human hair. There are also xanthophores, which produce yellow-orange colors, and erythrophores, which produce red colors.
Now for the color blue, you need something special- it isn’t a color the body can just produce through pigment. In the case of feathers, the actual physical structure of the plumes is altered to make a special reflective structure. In skin and scales, it requires iridophores or cyanophores, which are actually filled with compounds that physically alter the way light is reflected. Now in both cases, for the blue to show, a layer of black pigment (melanin) MUST be present underneath. Without the layer of melanin (or other pigment), the feathers/scales/etc will simply appear to be whatever the base color is, white or yellow or red or whatever.
So, using combinations of pigments and structural colors, we can create break down the colors of Twi’leks.
White- No melanin or other pigments present. Structural color may or may not be present, but will not show without melanin.
Flesh Tones- Varying degrees of melanin. No other pigments or structural color.
Red- Erythrophores present. No structural color.
Orange- Erythrophores and Xanthophores present. No structural color.
Yellow- Xanthophores present. No structural color.
Green- Xanthophores and structural color.
Blue- Melanin and structural color.
Purple- Erythrophores and structural color present.
Thus, it would be possible to predict the color of the children of Twi’leks based on the homo/heterozygosity of the parents for different pigment types and the presence/absence of structural color. But that is a whoooooole other talk in itself!
*Note, this also does not include rare pigment types select to a few taxa. For example, Turacos actually do have green pigment instead of yellow pigments + structural color, but this pigment (turacoverdin) has not been found in any other taxonomic group.