Expand sprite library assets to be able to color swap.

https://docs.unity3d.com/Packages/com.unity.2d.animation@2.2/manual/SLASwap.html
details how to color swap between the colors of the 2 different palettes of the imported images.

What would be very neat to have is the ability to import just a grayscale sprite, and be able to determine the color of a certain gray area directly in unity. It would be nice to be able to save the colors of a certain gray area in a kind of a preset, and maybe even save a colored sprite as a prefab variant.

It seems very tedious redundant to create copies of differently colored sprites within imaging programs, with the inability to quickly modify a color of a certain part down the line.

Can you make a custom shader in shadergraph and the sprite lit master mode to achieve what you’re looking for?

Give Shader Graph a try - in particular the Color Replace node. You could even convert everything from RGB to HSV so you can color replace a particular hue. This would allow you to replace a range of values, for example dark magenta to light magenta, with for example dark blue to light blue or dark red to light red.

Another approach to this problem would be to use sprite generation. Here’s an example: