As long as they are good quality, I really don't mind.
That said, the OCD in me would like them to match. Funny thing is, my current build is a matching Aero Precision upper and lower and they are not the exact same shade/sheen of black. Go figure...
Yes I like them to match. Although I have noticed over the years, with the Colt's of the '90's, their color match between upper and lower was always off. This was noticed by me, on complete new rifles. Some older Bushmaster's were turning purple, this was years ago.
I like billet receivers and a lot of time, the receivers from the same company match nicely but if you mix and match them they look good most of the time too.
So I guess it just depends. I have a Mega Billet upper and lower and the lines look pretty good. My Seekins mixes pretty well with my Spikes forged upper too but I do eventually want to get that receiver replaced with a Seekins, BRO, or maybe a Rowe.
On forged receivers, I at least like the lines to somewhat mate up, if they're from different brands I don't mind but I like them being somewhat clean.
Even slight color variations can be over looked. About the only funky thing that I'm not sure if I like or not would be having a BRO or POF upper or lower that was NP3 and having the other part black ano, not sure if I like that 2 tone or not
At the same time, is your rifle a safe/range queen, or a working rifle that actually gets shot with some regularity? If the former then matching is good, if the latter then it doesn't matter so long as it functions.
As I've gotten (a little) older, I've come to appreciate a rifle as a tool that gets dirty, nicked up, etc. as much as I appreciate a rifle or shotgun with fine walnut and impeccable bluing. Besides, a little Krylon and everything matches
Matched for color? The only time I've seen that matter is when you try to sell or trade it. Mine tend to be refinished in some type of camo pattern so it's never been relevant to me.
Matched by brand? Again, not an issue to me. Still haven't had a target come up to my position and demand to know the brand of my upper and lower in order to validate my hit.
Matched as to fitment between upper and lower? I worry about this one. On a loose, poorly fitting rifle, you can clamp the lower in a sled and watch your point of aim shift as the hammer strikes the firing pin. Does it matter on an ultralight M4? Probably not, but it becomes more and more relevant as you start stretching the rifle out at longer range.
Color match, yes. My OCD will permit nothing less. Though let it be said a designed color difference is OK, so if you had a burnt bronze upper with black accents on a clack lower with burnt bronze accents or whatever and it was a different color but still matched I would be OK with it.
If you mean by mfg, no. Quality is quality. Quality tolerencing is quality tolerencing and all the top companies will give you a nice fit. Just get it cerakoted or something.
Doesnt make me any difference as long as it goes boom every time I squeeze the trigger and is accurate. Both upper and lower color and even brand...no matter.
I would agree that the important thing is that it functions well, cosmetics are secondary. Having said that, I would include myself in the OCD crowd and would prefer for the make to match…. just seems right.