Assumes the sheet has no other color formatting on it, otherwise that will be deleted on first selection.
Code:
Option Explicit
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Cells.Interior.ColorIndex = xlNone
ActiveCell.Interior.ColorIndex = 6
End Sub
If you have any interest in highlighting the entire row (or even just a predetermined number of cells across a row) that is quite possible.
Also, you could have "Large Block O Data-1" and somewhere else on the sheet have "Large Block O Data-2" and when you click in either Block O Data the row will be highlighted from left edge to right edge of that Block O Data boundaries.
Might be more than you need or want, but FYI.
Regards,
Howard