(I'm one of the three people on earth who doesn't have Discord, so I hope it's OK if I post here) 
Some feedback: It's real good! The one thing I would definitely want to change is that holding the Alt or Shift key selects the Color picker (but only as long as it's held). I couldn't find a way to make that happen in the settings... Hopefully it's not to frustrating to hear about artist's pet peeves all day, sorry! :o
That's how I do it in Corel Painter and Aseprite so I'm very very used to doing it.
Once, I made a paint application for the terminal in Rust - what I would consider 'from scratch'. Obviously very tiny compared to your project and hardly usable, so the extensive functionality of Pixelorama is very impressive to me.
Best of luck with development!
