For those that have designed a tartan, is it ever OK to base a tartan on another tartan?

I am thinking of trying my hand at a tartan, but have been thinking of researching a bit for design ideas. As this would be a tartan designed for an organization, the colors are pretty much set. However I noticed the founders name is one of Celtic roots. I haven't looked to see if Scottish or Irish yet, but if it is Scottish and there is a tartan for his family, would it be out of the question to try and design something in the organization colors but close to or reminiscent of the sett in the founders family tartan? I have read that two tartans can not have the same sett, but I assume that means the same sett in the same colors.

This all may be a moot point if he has no historical tartan, but I thought I would ask before getting too far into this project. For that matter I am not even certain that the organization will want a tartan, but if nothing else it gives me a chance to try my hand at tartan design.