It is actually quite easy (Only reason i would know), if you look to the very right of the colors there are some letters and maybe there will be some numbers (e.g. #FFFAFA) but what these are is the code for making the color. See if you type |cff it will make the next 6 digits make the color. The first 2 digits after |cff make the percentage of red |cffXX----, the third and fourth digit make green |cff--XX--, and the fifth and sixth digit make blue |cff----XX. In case you don't know where this "|" key is located on your keyboard it is (or should be) located 3 characters to the right of your "P" key, but pressing this key by itself doesn't make |, you have to hold Shift while you press it.
If the key isn't located 3 characters from your p key it will just be the \ key...
