A Boa Mutation With The Color And Markings Of A Green Anaconda

[AbsoluteApril]

As for how to make those circle patterns black (and, possibly more circular) and the rest of the snake green, I don't have a clue!

You'd probably want to aim for making the saddles (the dark squares) into circles. The 'circles' you are seeing are the base color of the entire snake which is what you'd want to make green. I haven't seen the green color in boas (yet) though so that's probably trickier than the pattern. A rather common normal pattern variation is 'circle back ladder tail' CBLT, however it isn't always inheritable from the parents. Also look at the Aztec morph, you may like that pattern if you like motleys.