Well - having done some dipping into the more scientific side (IOW trawling for the last three hours through baffling scientific pages) - I found some interesting nibbles.
The salamander retina contains two or more classes of rod photoreceptors, mostly red and green.
It also has three classes of cone photoreceptors, red, blue, and ultraviolet.
The red rods are much larger, and the green ones are the smallest.
I would dare to suggest that whilst they have reasonable light/dark recognition, they would "see" red better than green.
Axolotl eyesight isn't particularly strong - however, you could try an experiment - train a 'Lotl to respond to one of two coloured cards, by feeding it when it goes to the "correct" colour card.
Swap them over every now and then so it doesn't get smart - and see if it learns the difference.
Try not to use red and green - they might be colour blind! *laughs*