I'd go further than your chief - the story is wholly improbable.

There are a good may two coloured tartans, too many to show but as a starter for ten:

Erskine
MacRae (not the standard sett)
MacDonald of Sleat
Menzies (Green & Black)
Menzies (Red & White)
Menzies (Red & Green)
Montgomerie
Rae
Rob Roy