What is the color code for CAN Bus?

CAN does not have a formalized physical-layer specification for conductor colors, or things like connector type or pin-out. There are common practices (like using a 9-pin D-sub connector) but no official standard.

Vehicles these days also tend to have multiple CAN buses, so colors will, of course, vary to keep the different buses straight. I have seen some buses adopt a solid color for CAN-L and a different color striped with the corresponding CAN-L color for CAN-H, to give a visual impression of belonging together.

Overall, as long as you keep track of your conductor colors and pinouts, you can use any color scheme that suits your preference without violating any standards.

I found a link for J1939 cables (not sure if this is generic): see link

Excerpt (see last two lines):

CBL-CAN-01: CAN Cable for DB9 Male Connector
    This is a 4-wire color coded cable. One end is DB9 female connector,
    it is designed to mate with Au J1939 products at bus side, such as: 
    J1939 Message Center System, J1939 Data Center System, 
    J1939 Simulators, etc.

The other side of the cable are 4 pig-tail wires.

Red wire: Power supply, +12V  
Black wire: Ground 
White (or Yellow) wire: CAN High  
Green wire: CAN Low

From 'John Deere' : Link

Red is Power - 12 V
Black is Ground - 0 V
Yellow is CAN High - 2.5 V
Green is CAN Low - 2.5 V

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.