Black background for back of tank

okay so today I put a black background one the back of my tank and also on one of the smaller sides that faces a wall. (in other words the corner) and now my fish seem unhappy -- is this a bad sign? should I remove background or will they adjust?

Update pics! I took the black paint off the back and got one of those cheap projection sun lamps for the blue background and I'm in love. (From now to hardscape 4

The blackwater tank, currently cycling. Got to get a black background set up! : r/Aquariums

Advice Please, On Black Background For Tank.

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Black background for back of tank

black background

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Shades of Aquarium Style: Exploring Black and White Background Options - PetHelpful