In some other engine I’ve worked with they allow you to pick colors while painting with any layers i.e you can paint your dirt layer with as many different colors you want. The color is multiplied by the paint brush. Since UE4 landscape layering is too limited in terms of performance that can actually be quite useful to be able to paint with a few layers but with custom colors so you can have variations across landscape.
Is it possible in any way to be able to paint a layer with different colors without having to create more landscape layers?
Don‘t know such things.But you can temporary create four more landscape layers and merge the layer weight into one RGBA texture after you finish the work.Then you can multi the texture channel with one layer to get the same result.
elaborating on the extra layers, you can make them NoBlend layers and you should still be able to have them on top of your regular layers.
I can see the pixel shader being quite cheap for this. most of the cost would be from sampling the landscape layer (and the fact that 3 more layers mean an extra weightmap under the hood) but I think overall the cost should be fairly low. no need to merge them into a texture later.
all in all the cost would probably be only ever slightly more than sampling an external texture for it, but [if your landscape is > 4k] you get the added benefit of having higher resolution compared to using a single texture