Shiny..

Hoo! Shiny Slowpoke are a slightly paler pink than usual. They're hard to spot, but it's a super rare encounter, so cherish it! You showed off some awesome work before, and your luck is just amazing, hoo!

Right, right! It gets a bit lighter! Once it evolves, the color difference will be more distinct. Congrats on the shiny!

The color is a bit lighter, but it's at a level you wouldn't notice unless you put them side-by-side.

The shiny one is a slightly lighter shade of pink, you know.

Congratulations! For comparison... the left one is the regular Slowpoke. As others have said, it's easier to see when evolved.