From The Setts of the Scottish Tartans by Donald C Stewart:

"The scheme of the red and yellow MacMillan is the same as that of the Wemyss and similiar to that of the Hunting MacLean..."
(All three are Hay-Allan creations, part of the bogus Vestiarium Scoticum.)

"There is a tartan sometimes called the MacMillan Ancient. This resembles the Buchanan, and derives from one of McIan's drawings, but as in the McIan-Logan work the MacMillan tartan is stated to be identical with the Buchanan, the making of a distinction between the two is pointless."

If I were a MacMillan, then, I would wear the Buchanan tartan, following Logan's 1831 symmetrical design:



rather than either the artificial modern modification of the erroneous 1843 McIan assymmetrical Buchanan, or the Hay-Allan "MacMillan" creation.