I need to choose the best match between a target color, and a list of RGB values that are available to me. In order to give the user a visual impression of the remaining color difference, I want to format the cells with the target and the best match using the RGB values in those cells.

I can easily achieve this by using a macro with a watch on the target cell. However, I prefer not to use macros. So, is there a way to achieve this without using macros?