Uploading Custom Shapes using GenerateBlocks Pro

I'm hoping to use some custom shapes on a project and I'm playing around on a demo site. I had two questions. First, what are the dimensions for the shape I should be uploading? I've only tried a couple of times but my shapes seem a little stretched and distorted. Secondly, is there a proper way I should be exporting this to get the color to change in the editor? Currently whatever color I switch to my custom icons and shapes stay black.