Saw a nice combination the other day: if you've got a hot purple Bougainvillea
that attracts a little too much attention, an effective way to cool it down is with the fast-growing Ipomoea tricolor (blue morning glory) vine.
The Ipomoea is a tender perennial best treated as an annual, but it blooms at just the right time to complement the Bougainvillea's colorful bracts. Plant one or two Ipomoea seeds near the base of the Bougainvillea -- they'll clamber on up through the larger, stronger vine, cooling down that bright purple while keeping the tropical effect intact.
Ipomoea seeds germinate best when soaked in warm water for 12 hours, or scarified with an emery board or sandpaper, prior to planting in early spring. Like Bougainvillea, Ipomoea resents having its roots disturbed, so it's best to sow the seeds in place (or, if you start with a container-grown plant from a nursery, handle carefully during transplanting).