Whenever using paint.net, my workflow includes using the colour curves feature to tweak the colours of whatever i’ve made; the fact that you have a visual representation (a curve) of waht happens to the colours is very intuitive, along with you being able to drag around nodes being responsive. In Material Maker, a different piece of software, there is a Colorize node that allows to map grayscale into a colour range by choosing intermediate points, and it serves a similiar purpose.
I feel like Pixi lacks a feature that’d allw responsive, intuitive, precise and swift manipulation of colour. There is palettes but they are clunky when it comes to switching around colours and aren’t as responsive (you can’t do teh equivalent of “dragging things to see how they look”); there is the color adjustments node which does allow you to drag and get instant feedback but it doesn’t allow precise local changes to the colour structure, and then you can either use shaders or modify image to modify colours manually via math, which is very precise, but not intuitive.
It’s hard to devise a feature that’d devise a feature that covers all use cases. The material maker example is a 1D (grayscale) → 3D (all colours) map, which is nice but gives you little control over the interpolation of colours. Paint.net curves have very intuitive interpolation, but at the cost of the three colour maps being separate 1D->1D maps. A 1D->2D system could be achieved with Bezier curves, but I suppose it oesn’t really have any significant advantages; if you asked me, I’d opt for a system like paint.net’s.