Since the snakes seem to be an important part of the game, i would suggest that you color them brightly. try some yellow and red and make them obvious. if you colored them green i think they'd blend in too much.
Love your work, very colorful. 
Thanks! About color not exactly, because snake mainly must creep on box and they is yellow-brownish range... and she is be green with black ))) See some image below.
At last, I am finish one animation of snake, i hope....

And paint tile basket for snake - it's my headache ))

This it's a without other tile, just view move snake forward.

Also you may see this move on field with other sprites

Yes, we cann't see her entirely, but snake must creep under other tile, differently it's look bad, not some realistic.