I was working a private pool party this summer, and someone asked for a pina
colada. I asked her if she wanted something a little more interesting, she
said "Go for it". I layered strawberry daquiri on top, and rather than just
leaving it there, I pressed my bar spoon down the side of the glass (spoon
side down) in a cross around the glass. It makes a "spike" of the red
dropping into the white in 4 places around the glass. I would imagine it
would work the same way for the 3 layers... except with a multicolored spike.
Try it out!