Clan MacNeil has only 3 tartans:

Clan MacNeil of Barra ITI 1767
Clan MacNeil of Colonsay ITI 196
These are the only two tartans recognized by the Clan Chief

Clan MacNeil Chief's Sett ITI 1839
This tartan is restricted to the Clan Chief. The current Clan Chief does not wear this tartan as he feels he should wear the same tartan as the clansmen.

The Scottish Tartans Authority also lists the following:
MacNeil Dress ITI 1974
MacNeil Personal ITI 3500
MacNeil, Royce ITI 7497
These three are not recognized by the Clan Chief. #3500 was designed and named by an individual without following convention.

As I am a MacNeil of Barra, I have only ONE tartan. Various mills produce it in a "Modern" dyes, an "Ancient" dyes and a "weathered" dyes forms. Still the same tartan.