Cell colour change to match that to its left

Hey everyone,

So as the title suggests, I would like a way whereby a cell automatically changes to the colour of the cell to it's left (or to a specific cell). So that when I change the colour of cell a1 for example, it will automatically change the colour of cells b1, c1 & d1.

I have attached an example document to help explain my point. As the first column may be merged and therefore I want all the cells to its right to be the same colour as it.

All ideas welcome, thanks!

Callum