Many of those colors are in the standard list of named colors. Then copy it into descriptor_color_flightrising.txt and use it as a template to fill in any missing from vanilla.
Don't worry if the RGB value in vanilla doesn't quite match the color wheel. No one will notice.
As for applying the colors to the creatures, you have different choices depending on the game-meaning of the colors.
Method 1: make one creature with two castes (MALE and FEMALE) if dragons reproduce normally in this setting, or don't specify a caste at all if they're just magical.
In the spot where you designate colors, include something like:
[SET_TL_GROUP:BY_CATEGORY:ALL:SCALE]
[TL_COLOR_MODIFIER:MAIZE:1:WHITE:1:ICE:1:PLATINUM:1:...]
[TLCM_NOUN:scales:PLURAL]
The creatures will differ only in color.
Method 2: Work out all the differences at the caste level, and in each caste give a single color option for the scales. If you want them to breed, you'll need two castes per color (unless certain colors are certain sexes in FR).
Both of the above options allow dragons of any color to breed (if they even have sexes). The hatchling's color will be one of the parents' in Method 1, and could be any color in Method 2. If that is a problem:
Method 3: Make a separate creature for each color, with one or two castes as appropriate. This prevents any cross-breeding, but you'll be unlikely to ever see more than one color on a map.