This is based on Mike's second Turtle Titan costume, seen during the "Lost Episodes" of the 2003 series. I had initially started using Playmates' Turtle Titan, but realized that the second costume was too different from the original to justify it. I ended up going with the standard Michelangelo and sculpted most of the details, adding Turtle Titan's cape and shield, as well as Nobody's grappling hook.
Either way, it could be the quality of the paints, or the thickness of them causing it to not come out as you would like.