Simple method, just desaturate, having color levels around 128 helps, but you can change the intensity inside the engine as well.
Complicated method is understanding how the blend algorithm works and then try and error.
What I do now is, I do not even desaturate fully, but leave some color in the detail texture, because sometimes having everything grey around 128 color level makes the texture look bad and unrealistic.
You have to understand that each texture layers color intensity gets added to the others, so you have to use your instincts to make the textures roughly neutral.