If after reading Jim's explanations
(you have looked at them haven't you? 
), you still see no difference in the shading, reflections and speculars (shine), then one sure fire way of instantly knowing if the effect is on or off, is to look at the caudal peduncle,
(... the bit between the body and the tail! 
) - particularly on the Emperor Angelfish, though on most others it's still very obvious.
If that doesn't convince you, then it's time for a new monitor, - or/and an optician visit!
ps, - The setting has always been permanent, - to the best of my knowledge!