BlendIf is very useful method in photoshop when you need to eliminate particular color i.e. white or black you can use blendIf.
Or this can be used to eliminate from below layer too as shown in photo below:
Or to eliminate colors as RGB change color mode from gray to Red, Blue or Green respectively.
It can also be used to remove shades of perticular color by holding alt key with mouse click.
This will be found in Layer Style in Photoshop.