Love the ‘paint all keyframes’ at once. That would be a life saver and the possibility to change the color for all of them.
Well, then you guys can go to WIP: Making colorize mask work with animation (!661) · Merge Requests · Graphics / Krita · GitLab and cheer the volunteer who’s working on it 
It’s of course about the Colorize Mask which works for sure differently than what you’re talking about here, but is about the same thing, to color animation. Since it’s a mask, you can attach it to a group layer where some layers will be actual lineart and some would be lines between the shadow areas and non-shadow areas. Then all would be considered together, and you’d just need to mark the shadow areas with the shadow color and the non-shadow areas with non-shadow color.
It’s still not ready, it’s not even merged, but it’s being worked on and some encouragement is always welcome 
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