How do you get a player's body a negative reflectance?

Hello, I am making a game that requires a players body to be darker than rgb 0,0,0. How would I do that? I normally just use a negative reflectance on parts and such that I need, but it doesn’t work for player’s body parts. Is there anyway that I can do that?

On the left is the -9 reflectance black, (RGB 0,0,0)
On the right is the normal rgb 0,0,0 reflectance set to zero for reference.

Is there a specific reason? I can’t imagine a color that is physically darker than RGB(0,0,0), are you perhaps trying to remove the specularity (shininess) of avatar parts? If so, you can try setting the colors to RGB(0,0,0) and set the Materials to Neon.

I don’t see an immediate difference between these two parts, and I generally wouldn’t rely on negative reflectance.