Heidi -
Any plant can exhibit a color break or change in color due to mutation or at times the colors of flowers will change due to temperature. The higher the temp the lighter the color usually is, the cooler, the deeper darker the color. If the pH of the soil changes it can influence color as well.
Do you have a Morning Glory vine that has two different colors on the SAME plant? They are usually not found growing singly by themselves - usually in a group with others of the same kind - by they way, those Butterfly Bushes that are of more than one color on the "same" bush are actually two or more different colored plants that are grown together, giving you a multicolored display. Great selling gimmick, but the different colors are not coming from the same plant.

Some Four-O-Clocks have striped and variegated flowers, some of which can be solid in one color and solid in another color on the same plant. I don't see why a morning glory couldn't be bred to do the same thing. There is as least one variety of striped morning glory. There used to be double morning glories, but I haven't seen them recently.

-- Burton --