There is also the Dutch Mackay tartan -- a little history of the connection:

The Mackays of Strathnaver are especially remembered for the famous "Mackay Regiment" raised for the service of the Dutch and Swedish crowns during the 17th century. As a result of this many clansmen settled in Holland and Sweden and gave rise to a number of noble families there. In 1628, Sir Donald Mackay was raised to the peerage of Lord Reay by Charles I. His grandson, Colonel Aeneas Mackay of the Scotch-Dutch Brigade, married the heiress of the Baron van Haefton. The Mackays suffered badly in the Strathnaver clearances between 1815 and 1818 and finally in 1829 the Reay estate was sold to the Sutherland family and in 1875 the chiefship passed to Baron Mackay van Opermet who became 10th Lord Reay. His nephew Baron Aeneas Mackay, prime minister of the Netherlands was the great grandfather of the present chief.

The Clan Mackay Chiefship is vested in the Lords Reay who also hold the title Barons Van Ophemert in Holland. Donald MacKay, Chief of MacKay, was knighted first Lord Reay.

-- http://www.clanmackayusa.org/Features/mkhistry.htm
The Dutch Mackay tartan is pictured here:

http://www.clanmackayusa.org/images/mktartns.jpg

Second from left.

The BBC is running this article about the new Dutch district tartan:

http://news.bbc.co.uk/2/hi/uk_news/scotland/4211272.stm

Cheers,

Todd