i am currently tryin to write an excel worksheet to add up the money i make from my weeks work, i have 15 minute slots from 9am til 5pm, and from monday to friday in cells a3 to a9, i want it to calculate how much money i make a day

i want £0 added to a cell if i have left the back colour as white/normal back color, while if i was to fill in a cell in a other back colour such as red i want £5 added to the total.

i dont want to use buttons for this would prefer it to just do it on the sheet straight away, any suggestions would be great cheers.