Peruse the available paint brush colour options for each species of Neopet. (It's our own version of the Neopets Rainbow Pool.) You can even see a list of which ones haven't been released yet!
The following biology parts can be removed with the appropriate Be-Gone! can (not applicable to Pet Styles).
Prior to April 2007's big revamp, Neopet colour combos were available in static poses, which you can see below:

Circle

Faded Circle

Happy

Sad

Angry

Sick

Petpage Photo

Close Attack, Left

Close Attack, Right

Ranged Attack, Left

Ranged Attack, Right

Defended, Left

Defended, Right

Hit, Left

Hit, Right
This Neopet was not available in Unconverted (UC) form prior to Pet Styles being released.
