Well, well, first answer in a while. Golly, has it been some time
yes, shiny slowpoke's colors have been changed. From the almost-indistinguishable-from-regular-slowpoke pink it was, the shiny's color has been changed to a purplish hue, which has it's shiny color back in the original GSC and in the Gamecube games.
Source: Has played all games since GSC, proud owner of a shiny living dex and this
Hope it helps!
