I'm not going to tell you anything you haven't already gotten in a response. My church has stools for musicians to use. Just plain ordinary wooden stools painted flat black as you planned to do. They seem to work fine, although the musicians don't use them anymore except for sitting down between songs since the gaps between songs can be of considerable length during a church service unlike those at a secular music concert.
I'm the one to blame for the no sitting thing!
When I first offered my humble skills as a bassist to this church they had me sit in at rehearsals with the band for a while. At the time all of the musicians played sitting down. All of them. But I played standing up simply because they hadn't put out a chair for me! And that is how I started to play the very first time I was actually asked to play in a service. At the pre-service rehearsal the keyboard player complained that I was blocking his view of the drummer so I offered to find a chair and sit down but the worship pastor would have none of that. He wanted me to stand because he felt the band had more energy if I did. And very soon he had all the musicians standing except for the keys, piano, and drums. After a couple of years even the keys players started to channel Jerry Lee Lewis leaving just piano and drums sitting down.
It's all my fault.
As for weight limits, I hear you. I'm only about 190 to 200 pounds and I look at things carefully when I am buying them because if I want a ladder and it is rated at 225 pounds it won't work if I have to carry more than 25 pounds while climbing it. As several of you say that is a pretty low weight limit for the fairly typical modern American male....
