Making an RBG chart on Excel
The expressions Int(256 / (Max * 2)) and Int(256 / Max) have constant values inside the loop. It would be good to save them in a local variable before the loop and reuse.

The line where you set the cell color is too long, I have to scroll horizontally to see what's on the right hand side of the line. You could improve that by putting the red, green, blue values in variables. I would also rename the current red, green, blue variables to redBase, greenBase, blueBase, or similar.

The naming of the loop variables Row and col are inconsistent in capitalization. It would be better if they were either both lowercase or both starting with a capital letter. Similarly, it would be better to consistently capitalize all keywords, like you did For and Next.