Buffalo grass spreads through above ground runners called stolons and also by seeds. The seeds are about the size of small peas, so you wouldn't miss them. It's possible that the plugs you got are from a female only variety and won't produce seeds.

What probably happened is that you planted before the soil was warm enough and/or wet enough for the blue grama and buffalo grass to grow so it sat there dormant (or semi dormant) until it warmed up enough and got damp enough and it's now growing from the roots.

Buffalo grass is somewhat gray green, so that's probably what you're seeing.

Blue grama spreads by seeds and only very slowly by tillering (a new plant comes up right next to an existing one). Blue grama seeds are tiny--like dust. Blue grama seeds grow on stalks that are higher than the seeds for buffalo grass. If you mow the plot, the grama will tiller more, but you won't get seeds. If you want it to look like a lawn, the grama may get too tall if you let it go to seed. But I think you'll get more spreading overall if you let the grama go to seed.

It will probably only be green from mid May until early to mid October. Both of those grasses are warm season grasses, so they'll be dormant longer than most lawns in the area. But once they get established, they'll probably stay green all summer with little or no irrigation.

Thank you for the info about the grasses. I'm definitely still learning!
Upon further reading, I think what happened is we tilled up the soil enough, and then it happened to rain enough, that weed seeds that were dormant suddenly had great conditions. So there is a lot of pulling and hoeing in the near future.