Some people think letters have particular colors because they have a condition called Synesthesia. A synesthete's brain tends to associate certain letters with colors.
The idea was to use some of the colors of the rainbow, however this would bring up controversy weather google is for the gay or that it supports the gay community, so to avoid speculation they decided to repeat colors on some of the letters.
lavender
Emerald
red and tan
CornFlower
They all have 3 letters, but "red" and "tan" have exactly 3 letters.
Brass is a color. It contains the letters B and S.
PINK BLUE GRAY
yellow, purple, indigo
Red? -.-
yellow, blue,
red, tan