I definitely agree and while I have not had this problem with him, I have paid Jim Steranko almost as much and had him insist on using black in a dark area while I was asking him to use a red paint pen that I was handing him. Due to this, I will not get more signatures from him in the future.
Steranko is a a great guy. I did have a similar situation too. I had a Nick Fury Agent of Shield #1 poster, that I wanted him to sign in silver, but he insisted on blue. The area I wanted him to sign was the darker blue area. We went back and forth for a few seconds. Trust me, Jim Steranko has forgotten more about the color wheel than I will ever know, but I wanted what I wanted. He finally caved, took my small cash purchase, signed it, shook my hand and I walked away.
He has a really nice signature, and it is subtle, not overpowering with the silver, which is what I wanted.