In nature, most males are the colorful one and the females are not as colorful. (not as pretty) Why? Because the males want to attract the females and mate. If you look at a peacock the ones with the "eye" feathers are the male (the blue ones) the brown non-colorful ones are the female peacocks. So my guess is that the colorful fish are the males and the non-colorful ones are females. But don't take my advice, I don't know I'm right! it's just a guess!
I hope it helped (even though it was a guess!
Most fish food will give fish a glowing color.
Fish tend to loose their colour when they are ill/sick. The usual reason or cause of fish becomming ill is poor water conditions or water parameters that do not suit the species being kept.
It's in their DNA.
angelfish
opah
Although I'm not sure what you mean by "deep" body, Betta fish, or Siamese Fighting Fish, or Rumble Fish (if you're S.E. Hinton) are thin, brightly-colored (domestically bred males tend to be more colorful), and have long, wavy fins.
Some different species of birds
brightly colored males:)
Because they are trying to warn predators that they are poisiness
To attract pollinators.
Cocks were created with brightly colored feathers to make them noticeable to females who may be attracted to the colors.
A brightly colored blanket or cloak is called a serape. It is worn in Mexico, Central America and South America.
i do not know sorry
the brightly colored petals help attract some agent like bees and insect which helps the flowers to polinate
Brightly colored males