Have you considered not using VBA, and simple Conditional Formatting. Try this, select from cell H5 down to as far as you think you will have data in column H. Then with that range selected with H5 as the active cell, click on Format > Conditional Formatting, select "Formula is" from the drop-down, and in the field to the right of that enter
=H5<>H4
Or, for the entire row, click the "5" row header and drag your mouse down to the row header that will be the last row of data. Now given the preceding steps above, in the Conditional Formatting dialog, enter the formula
=$H5<>$H4
Click the Format button, patterns tab, select the yellow square from the color palette, click OK, OK and that should do it.