Color is up to the town.

Green and white used to be “standard”, but green blends in with the trees.

Dark red or blue with white lettering is also popular. Some weird places did green signs and yellow letters.

My town switched to dark red (maroon) and white, since our school colors are red and black.

Recently the town looked at the lettering and ran some tests, and we’re switching to upper and lower case letters (rather than all uppercase) since they’re easier to read. (They’re replaced as needed, we didn’t waste money changing all our street signs.)