I got a Pikachu tattoo a few years ago, and after agreeing the design/placement the artist held up a series of coloured inks and made me do a binary-search, saying "This one, or that one?" and I think there were about six to choose from.To me it was obvious there was one correct colour for Pikachu to be, she approved of my choice and said "Ahh yes the original design" which puzzled me at the time, but I guess there a nuances to the shades and versions of characters like this, which evolve over time (pun intended).
As for me? Tattoos fade over time so the colour is different than it used to be, but everyone who looks at it knows exactly what it should be so that's fine.