I really like the "set colors" feature (but it's doing night cards like they're regular split types.)
I also really like that it's in hexcolors rather than multiplicative RGB, that makes it much more intuitive - load up the w3c hex color picker, copy-paste, ezpz.
Including different blend modes is interesting - I've mostly used those with
Jerry's Java Image Editor / ImageEditor.jar, which for a while was the only photoshop-like that'd run on my then-potato of a computer, so it's interesting to see them in a browser. Do you have the option to add like, Additive as a mode?