I take a knife (you can use a paintbrush also) and smear a stripe of the coloring paste inside the bag. Then fill with white (or alternate colored) icing.....careful not to smear. When you put your tip on, be sure the narrow part of the tip is aligned with the colored stripe. The first few roses will have a real strong edging .... the color will fade as you go.
I can't get to them right now to create the link for you (on the other screen I am getting the "website down for maintenance" message), but in my photos are a couple of sheet cakes with the 2-toned roses/rosebuds that I made this way.
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