How this works:
It takes the grey values from the
Shader to RGB Turns the data (casting in programming speak) into RGB colors.
Without this we cannot change the colors using a color ramp,
Color Ramp node remaps the grey values to the color you want,
Finally outputs it.
How it works:
This is essentially a masking material.
The texture going into the factor of the
Mix shader node is a grey value. It determines the mixing factor of shader 1 and shader 2. White color shows
Shader 2, black color shows
difference node (a mix node) compares the original texture to
color 2 (the color we want to remove when texture do not have alpha channel, black if it has alpha).
less than node (a math node) refines the edges of the mask using the threshold value.
diffuse BSDF node can be exchanged to
Emission shader for shadeless texture or a more elaborate setup.
Remember to change Blend Mode to either
Alpha Clip, Alpha Blend or Alpha Hatch. Which of these Blend mode you choose will depend on your use case.