Albedo values - use a pbr cheat sheet. Specular, start with 0.5 - it corresponds to IOR 1.45’ish and is adequate for any/most dielectric. Going 0.4 or 0.6 is not what is going to be what makes or breaks the appearance of the material. Satin and hair would be two good examples of specular tint towards base, because their actual geometry is far more complex than what we simulate with simple surfaces. Plastic? Not that I know of, I would use white. Many more? Not that I know of. There may be other processes at work that tints reflections (not necessarily towards base), such as thin film coatings, iridescence, or hazy gloss, but for dielectrics the “rule” is keep it white, and know why you’re breaking it.
Not sure what this means. On a flat plane (for simplicity) on creviced floorboards, I can’t just set diffuse to black for the crevice, that would still make it reflect specularly. I need to reduce specular to force it to appear dark. Just increasing roughness doesn’t do that.