How make UV Textured mesh with material instead of specific colour? Just trying to replicate table with epoxy. But can't figure out how to create a complex material.
I have a textured table top but can't replace black strip with a material.

Eventually, I wanna get something like this:


But when I am using mix shader it turns blue:




I understand there should be some mask but can't figure out how to do that.
Just figure it out. Need to add RGB BW and do some math rules, but would be glad if someone will present more correct or convenient way of doing that