What is your application? I think in most cases, industry uses international electrical code standards ("IEC("")":https://www.allaboutcircuits.com/uploads/articles/wiring-color-codes.png) in there wiring color coding.
article 504 of NEC, light blue is intrinsically safe, other than that your 24 VAC can be any color except green. Don't use white or grey either unless it's grounded, and make sure the wire is the type allowed for your application.
