on second thoughts, there's just 1 thing that is hard to differentiate for me, but I don't know if it has something to do with my red-green colour blindness. There are some champion abilities like Darius's 2nd and Morgana's ult and Riven's 3rd that don't have distinct colour to them, so it's easy to see them as greyed out i.e on cooldown when they're not. They look too similar to greyed out when they are ready. Since peripheral vision is often used to tell which abilities are ready, it can be easy to miss those abilities.