What two colors are most prominent in the attire of the "knight errant" and his horse?

I'm pretty sure both the Knight and the horse were green.

All I can think of is the famous green girdle was made out of green silk and embroidered with gold thread, both these colours are connected with the Green Knight.

The Green Knight and his foal were only attired in green. Green symbolizes a connection with nature.

"He was clothed entirely in green, and rode upon a green foal. Fair wavy hair fell about the shoulders of the Green Knight, and a great beard like a bush hung upon his breast."