How to add cells just based on their color background?

Hi, welcome to the forum

Your question needs a bit more detail (for me, anyway)

Are you asking to sum the values from cells that have a background color applied to them?
If so, then, sorry, excel cannot "see" color, so unless there is some logic to how the color was applied, then there is no formula that will sum colored cells for you.

If youi meant that you want to APPLY color to certain cells, then as suggested, you could do that with Conditional Formatting.

Please explain a bit more what you are trying to do