Red and blue is yet anothr variation on a simple theme. It's wrong per se to reference it to the Rob Roy as that name was a Wilsons' one for the Black and Red check that we know from portraits was worn widely during the Jacobite era, often as not by non-MacGregors.

I don't know your source for the R & B claim but there is a half torso portrait of Lord Ogilvy, attributed to Allan Ramsay, in which he wears a jacket of red and black check and a plaid of a slightly more complex sett. It appears on p26 of Hesketh's book but only in black and white and I've been unable to find a colour version on-line. Assuming that the portrait was painted from life, I somehow doubt that Lord David would have had another outfit in blue and red too and suspect that your source is in error.

Years ago I wove up some R & B check for hose and a waistcoat but wouldn't think of calling it anything other than 'red and blue dice'.