Nintendo's in-house emulators seem to be hit or miss. NES titles on the WiiU are notoriously murky; yet thankfully, the 'NES Classic Edition' doesn't suffer from that.

Edit: Although I can't find an official confirmation of this, it seems to be widely speculated that the murky colors found in the NES WiiU VC games was in fact an intentional aesthetic decision to help reduce the risk of epileptic seizures. It's further speculated that this was not necessary in the 'NES Classic Edition' due to rom hacking on the part of Nintendo to alter the way images flash on screen.