Hi Marcin, really thankyou for the kind reply, as I said I don't know Corona, I posted a question for a friend, so she tried your suggestion modifying the color of lightmix-Cshadingshadows channel, then importing it in photoshop as a layer over the original one, then invert-subtract-opacity10%, as she found in a tutorial, and the result is a slightly better image (but a bit more noisy), but it is far from my method I used twenty years ago with standard max renderer working on the shadow element, where I could easily and radically change only the direct shadows color. Here, she obtained only a very very pale, subtle blue tinting of the FULL image (areas in direct sun light included) and if she lows the layer transparency, the image gets very dark and noisy all across the board. I think the problem is the difficulty to isolate GI ambient shadows, absent in my old Max version. Maybe the right approach is to use hdri, or modify the original sun's or ambient shadows color instead of working with postproduction?