Any good colored plants other than mums?

Impatiens and Pansies are a good choice this time of year as they tend to like cooler weather, are fast growing and flower heavily with many different color flowered varieties.

If the planter is big enough you can use them as edge plants around the perimeter and plant something that grows taller in the center, like the Crouton pictured above or maybe some snapdragons that have nice flowers and grow fairly tall.

Wave petunias