From the above posting from Nigel:

"...in the late 18th century, the shamrock was adopted as an emblem by the Volunteers of 1777. But it didn't really become widely popular until the 19th century, when the emerging Nationalist movements took the shamrock, along with the harp, as one of their emblems. Viewed as an act of rebellion in Victorian England, Irish regiments were forbidden to display it."

What I deduce from the article is that Irish Regiments were forbidden to display a shamrock - they were not forbidden to wear green. As some one has previously stated there was never any legislation passed regarding wearing of green by anyone.

Come to think about it I will check, but I believe the uniform facings for the Connaught Rangers was green.