You could do it with conditional formatting (CF) ..
Example:
Select col A
Click Formatting > Conditional Formatting
Make the settings under Condition 1:
Formula Is | =NOT(ISBLANK(A1))
Click Format button > Patterns tab > light green > OK
Click OK at the main dialog
Try entering something in any cell in col A
The fill color "light green" will appear in the cell
For more info, try Debra Dalgleish's nice coverage of CF:
http://www.contextures.com/xlCondFormat01.html