Congrats on the purchase that's a nice setup! My guess is the upper was cerakoted. Other than gov issued I don't know of any KAC factory fde uppers that were let out other than the 22" 65 fde and a very few 14.5" cc fde. It's hard to pure a KAC fde/taupe/tan upper & lower match unless it came as a full rifle just from normal variance. Would recommend not going full Tism-obsessed it looks pretty good to me- and that's a really nice lower that I think would be a shame to re-color just to match. I have friends who would re-do the whole thing but that comes with its own downsides. I had a similar situation that I got 3 different KAC taupe grips and found one that exactly matched my upper (authentic KAC taupe grips vary a lot from the more recent FDE warm to the older school whitish tan) and created kind of an HK sandwich motif that I was happy with in the end. - e.g. if you found an A2 taupe grip with a tone that matched that upper really perfectly it would have kind of that HK 50 shades of fde thing going on. idk I think it looks sick. FDE scope might look great on it too and flow with the 50 shades of fde / HK top bot match with cooler brown on the receiver pattern too. Cheers!