16 seems to be the stopping block... I can get all but one, and I can even change the one that I can't get... Gonna have to go through each available path for all the colors before I can get it ironed out.
Edit: My goodness that took an awfully long time. You do not want to cheat, you do not want to get the 'easy' solution for this level. The amount of satisfaction garnered from placing that last square correctly is worth every second of frustration...
But if you do want to cheat, I have a screencap of the solution, PM me.