The transparency of stencil shadows can be set through mtl_shadow.alpha (default = 50), and their color can be set through mtl_shadow.diffuse_blue, mtl_shadow.diffuse_green, and mtl_shadow.diffuse_red (default = 0,0,0 = black).
those settings are for stencil shadows only, correct? I changed these settings, switched to stencil shadows, and was able to change the shadow colors. However these settings dont change the PSSM shadow colors.
ahh sorry. then you have to change the pssm shader. I remember once I made it for debugging the different cascades, not too tricky. but it's on my old pc, not yet ported my 3dgs stuff to the new one.