The Book of Kells shows leines of various colours e.g. red, green and blue. [I have a theory of which I'm having a difficult time proving, but I believe that the colors represented for or used to describe some of these leine were used for another purpose beyond strickly color. I find in quite a few texts that most of the mantles are green or crimson. Sometimes, tho they are refered to as green, the mantle is in fact another color entirely. Whether this theory ever proves out or not remains to be seen, but for now it's going to sit in the back of my head until I can find proof one way or another.]
The sleeves were wide or loose at the shoulder and tapered to a tight fit at the cuffs. There are no illustrations of wide loose sleeves at the wrist so it is a case of snips, needle and thread for any wide sleeves. The 8th century illustrations show the leine as a loose fitting, single coloured garment decorated at cuffs, neck and hem with bands of braid or embroidery. There is no pictorial evidence for two or multi coloured leini. The neck opening was usually circular with an occasional v shape being used. The plates of the Shrine of St Moedoc could possibly represent pleated leine as the folds seem too regularly defined for a representation of normal folds in cloth. As the shrine is 11th century it could possibly indicate a fashion or style change influenced by the Scandinavian pleated kyrtle. The leine was secured about the waist with a crois or belt. This was made of either tablet woven wool or leather and would also serve for hanging a pouch, knife or other articles. In warm weather or when engaged in work or fighting the leine would be 'pouched ' over the crois to allow greater mobility. The depiction of Cain and Able on the Cross of Muiredach at Monasterboice shows the leine being worn in this manner. Likewise a warrior depicted on the Cross of Scriptures wears his leine gathered. It should not be confused with a kilt for which there is no evidence.
On careful examination of the available evidence and in consultation with others, I have found no credible evidence that the Irish or Scottish Gaels gathered or pleated the sleeves of their shirts along the top of the arm. Leine is pronounced, very roughly, \LANE-yeh\, where \LANE\ is like the English word "lane" and the \y\ is like the one in the English word "yes". (http://www.medievalscotland.org/clothing/leine.shtml)
One point to bear in mind is that drawstrings in the sleeve of a leine is a contemporary development, coming out of American RenFaires in the 1960-70s Be careful what advice you take. (http://garbindex.com/content/leine.php)
Quoting from "Irish Noble Dress: 5th century B.C. to 17th century C.E." by T.H. Lady Lughbec ni Eoin (Nancy Lynch)
--"Styles and fashions of many differing centuries were worn side by side throughout the Middle Ages in Ireland. The Gaeils, being proud to display their connections to the past, traditionally honored their lineage by wearing garments to recall ancestral heros or events. Up to and including the Anglo-Norman period, just about any Irish garment style that was worn in earlier periods would have been worn by some Irish noble person. After the 12th century there were many confrontations regarding this custom and all other "things Irish" between the Anglo/Normans who had invaded the island country, and the Gaeil. Then in the 14th century the English=Tudors began strengthening the anti-Irish policies, becoming firmer with each succeeding monarch. Legislation, punishments, and even death sentences were doled out to those of the aristocracy and peasantry, both English bred and Gaeil, caught by those in power, wearing clothing or hairstyles "after the Irish fashion". The Tudor-English Crown was bent on Anglisizing and "de-Irishizing" all of Ireland."-- (http://www.geocities.com/Athens/Delphi/4715/costume/clothing.html)