Butterflies like purple, red, yellow, & pink. Hummingbirds love red as well. Butterflies like having water available as well- a dish or birdbath is good. Buddleia attracts butterflies. Its common name is butterfly bush. Asters, thistles, lantana, as well. Here's a site that lists the nectar sources for different caterpillars/butterflies.
http://butterflywebsite.com/butterflygardening.cfm