"COLOR" blend mode, what's the algorithm?

Hey there!
I’m trying to recreate a design in WebGL and i noticed some textures are using the “COLOR” blend mode. 
Is there a way to know what’s happening under the hood? I need to replicate it in `glsl` and so far i haven’t seen anything similar in these existing ones https://github.com/jamieowen/glsl-blend

Thanks!

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maybe ​@djv can help here?