That's what Motor-Viper, H.E.A.T. Viper, Strato-Viper, Frag Viper, Eel, Snow Serpent, Tele-Viper, Techno-Viper (or, appropriate for here, Gyro-Viper and Heli-Viper), etc. are for.
All of those guys being generics as well. My point is that it's not like Cobra is dying to hand out promotions, so I don't find it hard to believe they'd compensate by messing with the uniform and such. GI Joe has a two-tier structure consisting of greenshirts and specialists/unique characters, and I don't think it's going too far to think of Cobra as using a three-tier structure consisting of troops, Cobra Command, and guys in between who are better than the average soldier of their type, but not good enough to be in Cobra Command. There is actually support for this in the cartoon (Dusty and Claymore in 'The Traitor' seem to rank high enough to make using their helmets and masks optional) and in the comics (Scarface, who has subtle differences in his uniform compared to that of other officers). We even see this in the current toyline with the Snow Serpent Commander in the Arctic set (I maintain some of the stands were switched), and the Crimson Guard Officer and CG Leader.
Or, as I also said, even if you go with the assumption that it's a generic, maybe it's a training uniform that denotes this particular Viper is being trained as one of the specialty Viper types. I would doubt that a Gyro-Viper in training is going to be making formation with the regular Vipers, and this instantly identifies him as being something different.
I dunno. Maybe it's just me, but I can think of several good 'in-universe' explanations for why a Viper would be in this outfit. It's a lot better than some of the garish things we've bee exposed to in the past (just how effective are Alley Vipers in bright orange, anyway?), and I just don't have a problem with one Viper in a photo-negative outfit. Hmm... actually, I think I might call him Nega-Viper. I like the sound of it.
Generic? What do you mean?
According to all sources, EVERYONE starts at the "bottom of the barrel" and whether or not that is a Viper or a Blueshirt (the point is actually moot), your still starting off as basic infantry. You learn whatever specialization you need (missile specialist for the H.E.A.T. Viper, aquatic demolitions for the Eel, etc.) and you get a snazzy new uniform to denote your speciality. Once you go through the Eel training, you are now an Eel...not a Viper with flipper accessories.
To be honest, I think this guy is JUST a Viper (his filecard will be exactly the same as the normal Viper), no "training" version or anything like that. And that's what bugs me. Cobra had a LOT of interesting troopers (Rock Viper, Range Viper, Techno-Viper, etc.), yet we keep seeing TWO kinds over and over: Viper and Blueshirt. Ok, well 3 if you count the Joes that were used as Cobras (yeah, Barbecue). Even if they don't want to do whole new molds (which is weird to me as certain guys get whole new molds while others don't), they can at LEAST frankenstein some figures better than just a straight repaint. A Heli-Viper wouldn't be THAT hard to frankenstein with existing parts (BA Cobra Commander's body, Snow Serpent head, Deep Six's legs, IG Destro's arms). No new parts.....but a new character.
Part of my complaint is due to the fact that I REALLY do wonder if we will even SEE most of the "specialist" Cobras. There is a possiblity we won't based on some current trends. No Desert Scorpions on the desert pack. The "Bazooka trooper" (which is just a regular trooper with a fancy vest), the Night Watch set which didn't include any Night Vipers (or a S.A.W. Viper or Laser Viper, for that matter).
Maybe they aren't willing (yet?) to go that far (the farthest they've gone is 87). We are actually only missing ONE Cobra from 82 to 85 (the Lamprey), but there ARE a lot of troopers and individuals from 86 and 87 we haven't seen yet (Mindbender, more Dreadnoks, Motor Viper, Strato-Viper, Techno-Viper, etc. And the Gyro-Viper is an 87 figure as well).