The VBA code line you should use when you need to set a new background color to a cell is:
Sheets(“Sheet1”).Range(“C3”).Interior.Color = RGB(255, 255, 0)
RGB(255, 255, 0) = Yellow (full Red and full Green)
Where RGB defines the color you need as a mix of 3 color:Red Green and Blue (RGB).
Zero means no color and 255 means full color. Between 0 and 255 with the 3 color settings you can obtain any color you wish.
For other colors please see the color map article.