Sorry to burst your bubble but, it's all a myth made-up mostly by Sir Walter Scott and his like in the 19th century. The clan system only existed in the highlands and Islands and after 1745 it was destroyed for ever by the government in England.
To wear a clan tartan means nothing now - if it ever did. The only reason a distinctive weave was worn by a particular group was to identify friends and foe on the battlefield. Basically, you had to fight for the chief of the clan who owned your land and if his name was McDonald and yours Chisholm then too bad.
Here is a very good website that explains it all http://www.scotland.org.uk/guide/clan-system