Either is acceptable. Some people like the Oxford comma, others don't. It does help if you wish to reinforce the separate nature of the various colours.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
TclI like the colors green, blue, and red.I don't use the last comma unless there is something that follows that might be confusing without it.
or
I like the colors green, blue and red.