A detailed explanation of Papyrus in Undertale Orange:

Papyrus has tried a few styles over different timelines. Coincidentally, the colors always match the color of the current human's SOUL. (It's red in the original Undertale)

He actually uses his special attack (gaster blasters)

The orange human is the 3rd human (sorry, no Omega Flowey battle but I'll make a replacement), and Papyrus fails to capture them (at least not permanently), so he tries to capture all other humans that come later.

He has a bunch of spaghetti cookbooks on his bookshelf, because he is trying out a bunch of spaghetti recipes.

He still wants to join the royal guard, but Undyne isn't the captain (she's like, 10 years old in this, her mom is the captain right now)

His brother Sans is the exact same. (Not everybody has to change, right)