I am living only seven miles from Rathtangan and was unaware that there was a Colmey family in Rathangan until i read your thread. I will check around and see if i can dig anything up but i don't think there is any direct connection.
Would there be any chance it could be Kildangan?
It is not a very common name here in Ireland so there has to be a connection somewhere along the line.
Let me know if you get any more info or if i can help in any way.