The reason rhododendrons may "combine five colors in a single bloom" is because they can easily hybridize. If the flowering seasons of two species overlap, and there is a suitable insect vector, then cross-fertilization may easily take place between them. But such "indiscretions" are sure to come out when a single rhododendron plant bears flowers of different colors and patterns.
杜鵑「一花具五色」，因為不同種之間容易雜交，若花期相近，加上適當的蟲媒，好事自能順利完成，「偷腥」的事兒瞞不住人，同一株杜鵑常會開出不同色彩與班紋的花來。