Species: grey neopet
A Grey Neopet is one of the many special colours that a Neopet can be painted. Being more than an ordinary dye job, Grey neopets are distinguishable by being visibly distressed and forlorn.
In terms of lore, the colour can occur naturally if a Neopet is in despair for long periods of time, though this was intentionally not incorporated into the site's mechanics to not reward players for mistreating their pets . There is a heavy implication that this transformation locks them into that state of mind.
The population of several Neopian lands were turned Grey by a curse cast by Ozzy (himself a Grey Neopet) and Vira in "The Void Within" story arc. Pets under the influence of this curse have different symptoms than ordinary Grey Pets, as they keep their existing body type (e.g. a cursed Faerie Neopet will still have wings, but said wings will wilt and droop), and cannot be repainted, with methods of changing colour having no effect when used by them.
This tag implicates neopet_(species) (learn more).