I just took a pic of mine. This is what your aiming for
The coolant in there is 6lt of LLC concentrate & distilled water the rest so near enough to a 50/50 mix
The coolant & radiator cap in the pic are 4 years old and radiator 6 yrs
I have always used LLC (RED) and its clear enough to see the fins where the coolant passes through easily - ive never had any buildup of sludge / grime in the cooling system
Best to take the radiator out and have it flushed properly, my view is 'in car' flushes do not do anywhere near as good a...