Filling a transparent object with color

I am looking for the best way to fill transparent cells with a colour. I also want to preserve transparency.
Think of it as a progress bar that can change value over time and is NOT a 2D component.
I thought of changing the offset of a texture on each affected cell but given that these cells are sharing a material, is that the most performant approach?


You could write a small shader that could detect the partially transparent areas under a quad and mix the colors. If you want just two tones, have the shader define colors or textures for the two tones and detect if the pixels/areas behind it should be colored.