As a tailor, I do a LOT of basting, and there's really only one rule to follow as regards thread color: "Baste in white, always right." It sometimes happens that the bright, contrasty colors can rub off on light-colored fabrics, leaving little dots of, say, red, on your otherwise nice white shirt.
My gramma had a whole lot of other sayings to go with the above--"Baste in red, better off dead," "Baste in green, better not seen," etc. But it all boils down to--use white, 100% cotton thread. Synthetics can pull little holes in the weave.....
Stina