How do I change the color of this material?

Illidanstorm

I want to make this material a bit darker, but there is no option for it like in the usual iray surfaces that I know.

It comes from this product https://www.daz3d.com/the-coffee-shop

Richard Haseltine

You could try darkening the Diffuse map - one way to do that would be to click on its micro-thumbnail on the proerpty, select Layered Image Editor, and add a new solid colour layer, set the Blend mode to Multiply, and adjust the colour.

JonnyRay

You can also click on the Diffuse Map thumnail and choose Image Editor and adjust the gamma setting if you just want it to be darker. If you want to tint the color, Richard's approach gives you more flexibility.