Pardon me for being the historian in this post, but it is what I do for a living :

The Black Watch (The Royal Highland Regiment) were not in Ireland during the time of the Easter Rebellion in 1916, nor did they take place in operations against the rebels in the GPO in Dublin. There were elements of the Royal Artillery, the Sherwood Foresters Regiment, and some Irish units, like the Dublin & Munster Fusiliers, but to my knowledge, there were no Scottish Regiments deployed at that time. The Argylls, the KSOB's and other regiments did go to Ireland during the Anglo-Irish War of 1919-1922, but there were many English home county regiments, like the Sherwoods, the Essex, etc., as well as Irish regiments, that served.

The Ulster Volunteer (Unionist) Forces, the UVF, weren't even in Ireland in 1916 -- most of them enlisted in the Irish Regiments and went to the Somme with the 36th (Ulster) Division which got chopped to pieces on the first day of the Somme, 1 July 1916, along with the 16th (Irish) Division, which was made up of Southern Irishmen, including some Nationalist Volunteers who supported the Home Rule politician John Redmond.

The Black & Tans were not connected to the Black Watch in any way -- they were a special unit created by the British Goverment of out-of-work other-ranks (enlisted men) to assist the Royal Irish Constabulary in the aforementioned Anglo-Irish War, along with the Auxillaries, or Auxies, who were made up of former Officers. It should be stated here that these units were NOT part of the Regular British Army, but attached to the RIC, so they were essentially para-military police.

I honestly have never heard any of this about the Irish being "anti-Black Watch tartan" before. I have walked into a very Irish pub in St. Louis in a Black Watch tartan and never heard any of this, and this pub is a hang-out for the NORAID and other pro-Republican groups. Even if it is true, someone needs to do some reading about the history of the Black Watch -- it was originally formed to police the Highlands, not Ireland. The Watch has been to Ulster in recent times, but so have a lot of other units. And I would say that the Maroon Beret of the Paras would be far more unpopular than a BW kilt.

Now, as to Saffron Kilts: this is not just a "Northern"/"Ulster" thing: The Republic of Ireland's Air Force maintains a Pipe Band that wears a saffron kilt:

http://www.iacpb.org/home.htm

Pretty sharp uniform. I believe the "Rangers" in the Irish Army wear a saffron kilt as well. I even think there are some AOH bands that wear them.

The Saffron kilt was developed for the Irish Regiments of the British Army before the Republic gots its independence (like the aforementioned Dublin & Munster Fusiliers), but survives today in the Royal Irish Regiment, Royal Irish Fuisiliers, etc., predominately Ulster units -- but few realise how many Southern Irishmen still continue to join the British Army -- over 80,000 in the Second World War alone.

Most of the Southern Irish folks I have met have never been "anti-Scottish" or even "anti-English".

Cheers!

T.