Can you hear it? It's the sprites crying!
"We need more contrast, we're too hard to make out at 1x!! ; 3; Please fix us!"
Of course, I'm jesting, with the harsh tone and all, as a matter of fact, I think these small characters are absolutely wonderful! <3
The critique stands though, the all-coloured outlines make for a really nice effect, almost as if they were drawn with crayons (actually reminds me of kirby's dreamland 3), but you'll need to up the contrast quite a bit for them to be easy to see.