Highlight Selected Cell without Clearing Current Cell Color Formatting

Question

I have a workbook with multiple pages. I have formatted the color of many, but not all, cells and want to highlight the selected cell but when clicking off return the cell to the previous colored formatting. Let's just save on a single workbook cells A2:D20 are formatted with a green background. When I click into any of those cells I want the cell to highlight yellow. Once I escape out of the cell I would like it to return to the green color.

Thanks!