Private Sub Worksheet_SelectionChange(ByVal Target As Excel.Range)
Static OldCell As Range
If Not OldCell Is Nothing Then
OldCell.Interior.ColorIndex = xlColorIndexNone
End If
Target.Interior.ColorIndex = 6 'yellow
Set OldCell = Target
End Sub
This is sheet event code.
Right-click on the sheet tab and "View Code". Copy and paste into that
module.
Chip Pearson has a great add-in named Rowliner.xla that will make the
highlighting available for all sheets and workbooks.
The code above was cribbed from Chip to start with.