Here are the option of what Clip Studio haves. I think I'll use "Target All Color" one mostly for my Suggestion. And use "Area Surrounded by Transparent" as well.
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Am I doing it correctly to Stroke Fill existing color on color on TVPaint? Like Clip Studio can? Here's the example below on "Target All Color" on Clip Paint.
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Also is there's another thing on Fill. Can you tweak on "Expand" to be more accurate? I don't think it's accurate enough. It needs to be two decimals places for more accurate filling.
I'm dying for an update on TVPaint.