(mix color) bias amount based on a certain value?

[roughsporty 0]

I want to mix the color output of the ramp with the color output of another ramp based on a certain color range. For example, the second ramp should only mixed in if the Cd value of the first ramp is less than 0.1 (the whites only). So I thought it would be possible with the color mix node but I don't know what variable to put in into the bias amount. Or is there another way?

[magneto 148]

You can use the Luminance VOP and use your first Cd, and then plug the result into bias.