I just melted the butter at around 50 degrees for a couple of mins, then added in some icing sugar and strirred it on about speed 1 till it was blended
just add in the cocoa or whatever colouring you are doing, should work out
as you can tell I just made it up without really following a recipe as such
the one thing I did find was that the icing kept going hard so had to keep warming it up again