Re: colours and rank/wealth. Obviously the more money you have, the better access you have to rarer dyes and fabrics. In England this resulted in sumptuary laws, designating the particular dyes, fabrics, and furs one could wear based on their station. A merchant might be wealthier than a duke, but he still couldn't wear the clothes that the duke had to go into debt to pay for. You still can't dress above your station. The most famous of these laws is the limitation of purple (and various shades of blue - hence the shade of "royal blue") for the royal family.

I don't know about the laws/traditions of various tartans, so I'm not even going to weigh in about that. Given the historical use of woad in northern Scotland, I'm sure that blue had play here, though most traditional tartans I can think of are mostly based on reds and greens.

Andrew.