Your observations of course are exactly correct. I watched your video, your keyboard way to modify the color on the brush is nice! and the notion of tapping speed affecting the size of the incremental change seems like a very natural and efficient way to control changes in paint color.
Speaking just for myself, I never found any of the various RGB-derived color spaces particularly useful for picking colors, and I wanted something that would make it easy to put McEvoy’s information to practical use in the digital darkroom. High bit depth GIMP now has LCH color pickers and blend modes. LCH isn’t JCH, but it’s a lot closer to being perceptually uniform than XYZ or RGB or any of the various RGB-derived color spaces.
With respect to step-size, according to chilliant: RGB/HCY in HLSL, HCY “Hue” is the same as HSV Hue (and also HSL Hue). The HSV/HSL/HCY Hue ring makes it look like these Hues are spaced apart in some sort of perceptually meaningful way, and also makes it look like every color on the outer ring has the same “chroma/saturation/etc”.
But when plotted in the LCH color space, it’s obvious that these RGB-derived “Hue increments” in fact are not perceptually uniformly spaced at all, and that the maximum LCH Chroma for any given HCY/HSV/HSL Hue does vary considerably from hue to hue as chosen using the RGB-derived color spaces:
You picked one of my favorite pages from MacEvoy’s (not “Lindbloom’s” as I originally incorrectly typed, though Lindbloom’s website also is a great source of information, but about color spaces rather than about mixing colors) wonderfully informative website. Awhile back I put together a tutorial on using LCH to pick warm and cool colors:
There are some threads on pixls.us concerning LCH:
It could be the case that for MyPaint considerations of computational speed completely trump making actually perceptually uniform “step changes”.
Thinking ahead, if/when MyPaint is color-managed, and/or when Rec.2020 monitors reach the consumer desktop, all the intuitive grasp that artists have built up over the years regarding what happens when making color adjustments using HSV/HSL/HCY/etc will need fairly drastic “recalibration” as the meaning of triplets in these RGB-derived color spaces will change fairly radically when switching from sRGB to Rec.2020.
Right now MyPaint is not color-managed, so presumably the user is working in sRGB, using a monitor that’s more or less calibrated to sRGB? Why does HCY seem to use the “Y” values for NTSC (chilliant: RGB/HCY in HLSL)? The babl HCY code also uses these NTSC Y values. See Side Note 1 on this page: http://brucelindbloom.com/index.html?WorkingSpaceInfo.html