solved - easy way in affinity photo is to open the swatches panel, then in the options you can import a palette from an image, and you can set up to a 256 color palette. So you can composite a few images together that have the colors you desire. Then just set the display size of the palette to large and screenshot the…
its quite simple to implement, the effort is in setting the rules around what a material ID means. It's no more complex than dealing with a single indexed color palette but we stopped doing that for a reason..
Well when bringing in a reference image you could for instance create little dabs where you want to extract the colors from. Overall what I am trying to get at is that going for a "real" palette directly can prevent this kind of flexibility. But that said it seems to clearly work well for you, so my point is moot really :D…