Congrats on the new fish. Red Devils are Central American, so this post may not get much of a reply until a mod moves it to the correct section. Your fish should be fine, the colour is most likely natural, but a 40gal tank is going to be too small for it for life. If your fish is a female, a 55gal tank would a bare minimum for just the one fish, or if it is male, a 75gal would be the minimum. I'm curious of the dimensions of your 40gal tank as well, but I don't think any dimension a 40gal could have will be enough to keep the fish in for life.