Too many insightful things mentioned so far on this thread to bring them all in as quotes.
How it makes the players feel is definitely real. You can dismiss it a pre-game pep talk-in-polyester, but it boosted the emotional anticipation level of the players. (Which, on the flip side, may have played a role in the 2nd half drop off. Up until yesterday, the team's focus has been entirely on performance, in-the-moment focus, fulfilling assignments and playing with speed. The anticipatory high from the uniforms taps into a different dopominergic pathway from that of reward from accomplishment--i.e., the difference between the feeling from having successfully rebuilt the engine of a '63 'vette vs. the feeling of anticipating being seen driving around in a '63 Stingray convertible.)
That it improves recruiting is also evidently real. Heupel's professional personality seems closer to a manager/engineer than a showman. If he says it helps recruiting, then I believe he has objective evidence to back it up. One thing we keep hearing is how much players enjoy playing for and with this coaching staff. Bending traditions to offer players a new gameday experience gives visual expression to that behind-the-scenes reality. And it generates social media comments among potential recruits.
Black under sunshine absorbs radiant energy. That extra heat is not a competitive advantage, unless air temps are below freezing.
If the guys respond to looking like action movie or video game characters, then matte-black helmets would definitely better complete the look.
The unis had too many shades of orange, at least on TV under daylight. The jersey numbers were red-orange, and the pant stripes looked nearly yellow. It's a nightmare for quality control, because different materials require different dyes or tints, and each looks different under different light sources and from different distances. (I have a pair of poly-blend slacks that are smokey gray under the light in my closet, but are green in sunlight! The silk or wool ties they match inside do not match at all outside. It's another good reason to just stay in bed.)
It could be that they used the same orange paints and fabrics as used on the white unis, but their inherent differences were just magnified on TV against a black background. I've no doubt the colors would look differently under cloudy skies, and differently still under stadium lights--and maybe differently again under different stadium lights (unless the gods of ESPN have mandated that all stadiums use the exact same light sources).
My last comment is to offer objective confirmation to a subjective observation. Having had a career in graphic design, it's just a fact of color harmony: Tennessee orange (#F07900) on black is not pleasing to the human eye. Against black, the redder the orange, the worse it looks; the more yellow the orange, the better it looks. In the science of color harmony, Tennessee orange looks best against white, and against lighter, warmer grays (thus, the "smokey gray" attempt to create a compromise).
But, good or bad, color harmony is only relevant to observers, not the men in the arena. Our players logically enjoy wearing a look that is disruptive, chaotic, and violent. So what is a fault for the observer's eye becomes a feature for the players wearing it.
There are some ways to make the black uniforms appear more harmonious. Some of them have already been voiced here.
But I'm wondering if the fashion eye of young people may already be shifting away from the Marvel Universe techno-complexity of CGI, toward simplicity--from appearances to values. If so, maybe we end up with a black uni that's more retro--maybe not retro all the way back to horizontal stripes, but just black, with a black helmet, and a narrow white outline around the orange numerals.
Now: for the fan, does it "look like" Tennessee? No. This brain has been hardwired by 50+ seasons to associate orange & white with the Volunteers. Watching the game replay (having heard the game on radio) was noticeably not as satisfying, because I had to keep reminding myself that those strange looking players were my Tennessee Vols. And that's not something to easily dismiss! If suddenly your mother or your wife looks like someone completely different, you're not going to experience the same feelings when you see or hug them. And becoming a football fan is all about how it makes us feel. So doing this occasionally for the players is probably the best compromise. After all, for long-time VFLs, winning is Tennessee's tradition, as much as wearing orange & white.
Regardless of our individual preferences, players repeatedly performing and acting like winners can eventually imbue any alternative uniform with VFL pride. That's as it should be, and what we all wish for the generations coming behind us.