I'm not entirely sure what the issue may be, it could be several things. I used GIMP when i was working on stuff with Pix64. I've checked out pixilart.com, maybe try starting your image as a 64x64 image, that way you don't have to worry about resizing. Also, it looks like at least the red on pixilart.com isn't the correct red for Pix64 so you may want to make sure to update that(if you haven't alright anyway). I don't want to make any promises, tinytex64 may be able to help convert your images to the right size and palette pretty easily. The final image may need to be edited some as the pixel filter was a quick rainy day project and i think even without a frame or text it puts the forward button that would need to be edited out. I'm excited to see what you've come up with Llamahead56 =)