This is a characteristic of Japanese Satsuki azaleas. They have different colored flowers and flowers that have different patterns of the same colors on the same plant. They have R. indicum in their breeding just as the Belgian Indicas do. In fact many people call the Satsukis Indicas.
Kusudama:
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Aozora:
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Geisha Girl:
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Haru-Same:
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Lavender Lady:
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Nuccio Razzle Dazzle:
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Nuccio Razzle Dazzle:
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Nuccio's Voodoo:
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Yugiri:
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or could you be thinking of 'george l. taber'?
that one will sport(revert) the occasional solid purple-flowered branch. the majority of the flowers will be two-toned (pink to me, though i think it is classified as a lavender) and that could be seen as 3 colors on the same plant.
it can also produce a solid white-flowered branch, which is where 'mrs.g.g. gerbing' originated.