see here (RPG section the ctrl+f pokemon) and yep, nothing but simple palette swaps.
this "shiny" fan term annoys me every time i see it. it's likely most commonly seen in pokemon but i doubt it's exclusive to pokemon pics.
perhaps for things like OC's that are merely recolors yet otherwise look the exact same as the original character(s) in question (clothing aside if there happens to be any present), a palette swap tag could be of use?
Updated by Furrin Gok