IIRC an Excel aficionado named Ivan Moala developed such a utility about a decade ago. It would highlight the entire selected column & row, then restore the original formatting once you moved to another cell. IIRC there was a noticeable delay when changing cells, as the code had to: a) search the entire column & row for any existing highlights, so they could be saved; b) restore the highlight states for every cell in the exited row/column; c) re-save the highlights for any cell whose column/row overlapped the previous active cell's column/row; and, finally, apply the temporary highlights. Even that didn't try to preserve existing highlights while the column/row was 'active'. With modern workbooks having so many more rows & columns to handle, I wouldn't be surprised if the task became unmanageably slow.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]