Tough question, one that might generate a fair amount of discussion. I'm not sure deviation from the original color code
per se is all that bad; IMO, what's far more important is that -- to maintain or even possibly enhance value to some sellers -- any color change is as complete as it possibly can be. That means any painted surface even remotely visible, including at the very least under the hood and inside the trunk, is the same color as the outside. Practically speaking, this really is only doable during a complete down-to-the-bare-body, off-frame restoration.
This might not be quite so critical when going from Royal Blue to Sapphire (Imperial) Blue, but going from Java Green to Pimento Red is quite another story!
