Tartans for many non-Highland families have been registered in modern times and even many Highland Clan tartans are themselves very recent.
as per www.tartans.scotland.net
The accreditation list gives the author and weaver, James Scarlett, as the designer in 1980. The tartan register records the designer as Peter MacDonald who worked as a weaver for the Scottish Tartans Society in 1981. Rennies, Rainys and Rainnies (from 'Ranald') are listed as a sept of MacDonell of Keppoch.