I'm not sure if I understand the questions right..
Have I used a computer chair as a prop for my self portraits when they're in black+white or in colour?
No, I have not. It's because my computer chair isn't that stylish, and it's located in the basement of my house, so it's a pain to bring upstairs. When I'm taking self portraits, I use different props or stand instead of using a chair in the first place.
And no, due to the reasons stated above.
I'm not sure if these are the answers you were looking for but..