Quoting your post since you had this issue.
Played my Jedi Knight and noticed how to tell if my ability was usable on the next gcd.
Whatever your keybind is, be it 1, 2, 3, 4, 5, F, T whatever it is. If it is not usable on the next gcd, it will stay dull, but if it is usable, the number will light up as the gcd ability is active.
Hope this makes sense.
To the people who get headaches, are you epileptic? Do you go to a club and complain?