API support for adjusting artmesh screen colors

[darthmarth37]

At present a ColorTintRequest can apply multiply colors to ArtMeshes, but no such API exists for adjusting their screen colors. Making it possible to adjust them both, preferably in the same request, would offer plugins more flexibility with color adjustment so they aren't limited to just darkening.

[lualucky]

I believe you mean "screen" not "mask"