Is there a specific paintbrush that my Neopet needs to be painted in order for me to pull the lever?
No, there isn't a specific paintbrush, there are just certain paintbrushes that won't work in The Transfabulator. The Transfabulator cannot be used with unconverted Neopets or the following painted Neopet body types: Maraquan, mutant, baby, invisible, and fruit and vegetable Chias.