Why??

Fish change colors for different reasons. Matching their background is one: dark colors to blend in with dark wood, etc. Another is stress, or aggression. Fish will change color to be intimidating, or to look angry and chase off an intruder. Lighting is important too--more in SW fish, but in some fish, they change color at night, and then go back to normal during the light. Many fish also change color when they are excited--getting a really tasty treat, for example.

For clowns, it could be mood--if the tank parameters are in good shape, it's probably nothing to worry about.

My flying foxes are always pure white first thing in the morning. As are my gouramis. Crazy to see but they start to colour up when the lights are turned on.

Lots of fish change color at night and its not unusual to see pale fish in the morning.

With the clowns, I think that duskiness is an age thing. Just don't know why I think that. Wasn't mentioned at loaches.com, but I imagine someone over there would know for sure…