First off, I'm new to this... But every time I add Wilton color to my buttercream I get halfway through a bag decorating and the color seems to break apart from the icing and pools up in the bag. By the time I get close to the end of the bag it's almost syrupy, and everything has a tye-died look to it. So far I have been icing predominantly white or chocolate cakes with color accents so it hasn't been a huge deal, but I'm tired of being limited to that.
What recipe buttercream are you using?
I'm using the one in the Wilton course books- off the top of my head...
1 cup butter/shortening combo
1 tsp flavoring
2 tb water
4 cups powdered sugar
Let me guess, you added alot of color to make a darker color?
This happens to me, with Wilton colors and with Americolors. I believe that adding alot of coloring to icing thins it down and throws off the balance of the liquids off. I simply just add in a spoon or so of cornstarch to the icing while adding the colors for dark colors and it fixes it.
It never seperates until it gets in the bag and you go to use it. Not sure why.