This is a whole lot more than just adding coloured triangles on cells - font colours and sizes too.
I see there are formulae in many ofthe cells; presumably you are asking users to overwrite formulae. If that's the case, can we assume that only cells without formulae need to be considered for triangle addition? Can we also assume that all cells which still have a formula in them need to be white font? If that is so, does that font need to be white before the teacher is given the sheet for filling in?