I am not claiming that being a Scot from Scotland gives me any more credibility than anyone else, but never the less, for what it is worth my opinion is that folks should wear whatever tartan they like regardless of family connections or whatever. Furthermore, for those folks of any nationality or color, I say wear the tartan if you like it. Folks who just love to wear the kilt should be free to choose their color preference. Besides, since most of us seem to have more than one kilt, it would be dull, to have only family-connected tartans would it not? What is important I feel is that you should know which tartan you are wearing at all times so at least if a stranger asks you, you can make conversation about it. (doesn't it keep it more interesting?)
An American from Texas wandered into a kiltmaker on Edinburgh's Princess Street to inquire if there was a tartan for him. He gave his family name to the kiltmaker as Firestone. "Ah yes sir, I am sure that we have a family tartan for you sir!" said the kiltmaker and presently produced a nice-looking swatch. "and what is this tartan?" said the Texan somewhat surprised.
"That sir, is the MacIntire tartan" said the kiltmaker. "You mean that I can wear the MacIntire tartan, is that true?" "Ah yes sir, Firestone has been MacIntires for years!" replied the kiltmaker.
-Alan