How to create a colour overlay with the overlay node?


So I want to create a material that uses a colour overlay texture to add colour to certain parts of a model to create a weathering effect.

I have my Albedo (A) which is a full colour texture.
I want to overlay another texture (B) that is mainly grey with sections of colour.
The aim was to have only the colour parts of (B) affect (A), with the 50% grey areas having no effect.
What I’m finding is that the areas that are 50% grey in photoshop on (B) will darken (A)
If i set the grey areas to be 186 value in Photoshop then this will cause the grey on (B) to have NO effect on (A)… the effect I’m looking for. The only trouble is that the colours in photoshop all now look different as the are blending with grey 186 and not 128.
I need to use the colour blends in photoshop to get the effects i need in the texture…
How do I go about this?..
It seems like something really simple but is causing a lot of headache.
Any help or advice would be much appreciated :slight_smile: