As others have said, it is open ended unless you define "colorful". A yellow tang is very bright yellow, but so are other fish. Flame angels are bright red, and I think they make tanks look more colorful than yellow tangs since not many fish are red. Something like the lineatus bonomo53 posted could be considered more colorful because it is multi-colored or considered less colorful for the same reason.
I would not underestimate damsels for adding color. Those $5 electric blue fish are hard to beat.
I just had a tank crash, and am going to pick out new fish with my wife. Her number 1 criteria is she wants colorful fish.
So far I bought:
1) Harlequin tuskfish
2) Flame Angel
3) Annularis Angel
4) Coral Beauty
I really wanted to pick out fish with her, and I will for the rest, but we haven't had time and it is so depressing coming home to a huge empty tank.
The rest of my fish wish list (to steer my wife towards):
Yellow Tang
Hepatus tang
Blue throat trigger
Ocellaris clown
damsels (pomacentrus or chrysiptera)
anthias (pleurotaenia or squamipinnis, mixed feelings due to maintenance)
fairy wrasse
red coris (but I don't want to add sand)
longnose butterfly
flame hawkfish
toby puffer
squirrelfish
Liopropoma/basslets
If you have a 90g SPS, 46g LPS, 29g nano, your fish selection will very different than mine. Have you looked into a Catalina Goby? This is the perfect fish for someone who wants colorful in a very small tank, if they can keep the water colder.