Hmmm. Whoever Mangasaurus sourced for One Piece did shitty quality scans, they're clearly blown out compared to most sites. Makes it not worth it even if they are PNG's.
No, it's not original, but the color schemes are decided by Oda (the creator) and it really adds a lot to the manga. Colorized is best in this case, especially for taking in the immense world, which is one of the strengths of One Piece.