Great effort and reason to create this! I'm accustomed to using the Magic Wand tool in Paint.net[1] and Pinta[2] to select pixels based on color. Any chance you could add that functionality?
It lists Magic Wand under Features
[1] https://github.com/groverburger/grobpaint/blob/e249c7553f4c8...
Yep, magic wand already exists with contiguous/global toggle and tolerance slider. : )