with the way genetics are set up at the moment you will see very little diversity between each caste member.
In a regular game of dwarf fortress you will have two castes, male and female.
Most males will look mostly the same with only very few members diverging from the norm. With things like dwarves this is not very noticable, but if you take the pony mods for instance, where appearance is a lot more important, this becomes more noticable.
As Hugo mentioned below to fix this you simply duplicate your castes to add more diversity. Note that you will still need to make give the males the [male] tag and the female the [female] tag.
After you've defined your creature we first need to create a new caste. This is easily done just by entering the [caste:x] tag with a unique name
[CASTE:MALE1][CASTE:MALE2][CASTE:MALE3]
[CASTE:FEMALE1][CASTE:FEMALE2][CASTE:FEMALE3]
We have now created the castes, we can now define them using [SELECT_CASTE:] and SELECT_ADDITIONAL_CASTE:]
this means we only need to type the caste code once. If you just want more variation in your color spread and not specific castes have specific colors, you can just add the colors to [SELECT_CASTE:ALL] each caste will pick a random color from the available options, and most members of that caste will generally have this color.
[SELECT_CASTE:MALE1][SELECT_ADDITONAL_CASTE:MALE2][SELECT_ADDITONAL_CASTE:MALE3]
[MALE]
[SELECT_CASTE:FEMALE1][SELECT_ADDITONAL_CASTE:FEMALE2][SELECT_ADDITONAL_CASTE:FEMALE3]
[FEMALE]
Doing this we make our selected castes the correct sex
[SELECT_CASTE:ALL]
SET_TL_GROUP:BY_CATEGORY:HEAD:HAIR]
[TL_COLOR_MODIFIER:RED:1:BLUE:1:GREEN:1:YELLOW:1]
[TLCM_NOUN:hair:SINGULAR]
[TLCM_GENETIC_MODEL:MIX]
And bob's your uncle!