I would have thought the color would be based on the meaning of the sign rather than the origin of the constellation's name.
For example, Aries are considered impulsive, assertive, initiative-taking, so red.
Going quickly:
Taurus is about comfort, emotional and material, green.
Gemini are social, flighty, communicative, blue-red.
Cancer are nurturing, sensitive, green-white.
Leo is about leadership and idealism, red-white.
Libra is fair, thoughtful, polite, white-blue.
Virgo is detailed-oriented, practical, helpful, white.
Scorpio are passionate, secretive, dramatic, black-red.
Sagittarius is adventurous, curious, optimistic, green-blue.
Capricorn is traditional, ambitious, hard-working, black-green.
Aquarius is idealistic, individualistic, future-oriented, blue-red.
Pisces is romantic, dreamy, compassionate, red-white.
I would have liked to have not repeated, but I feel like Gemini and Aquarius both fit blue-red, just differently. I guess you could do the scheming, duplicitous interpretation of Gemini and do blue-black. Pisces, I am maybe least sure of, but it's relying on the emotional sensitivity of red and white.