The ISO 11898 standards do not mention practical things such as cables and connectors.
The second-most authoritative source has therefore become the CANopen standards, where DS303-1 specifies things such as standard connectors, pin-outs, cable lengths, baud rates etc. Unfortunately, this document does not mention color-coding either.
Yellow and green seem to be commonly used, though I have seen yellow mean either CAN High or Low. However, just because these colors are commonly used, it does not make them more correct.
I'm guessing that the yellow and green comes from the universally standardized color-coding (same as we use on through-hole resistors). That is: 1=brown, ... 4=yellow, 5=green. For the "mini style" and "micro style" (round M12-like) connectors standardized by DS303-1, CAN High happens to be on pin 4 and CAN Low on pin 5. From DS303-1 7.2:
This enumeration is however not at all consistent with other common, standardized connectors such as d-sub, RJ45 and terminal socket.