Some of the plants that I rely on to heat up the summer garden include:
Yellow Rudbeckia or Black-eyed Susan Orange Russelia or Firecracker plant Red Rocket Russelia Hardy Red Gloxinia Purple Coneflower Deep Purple "Dubonnet" Buddleia Verbenas from hot pink to dark purple Lantanas, especially "Dallas Red" with its rose, coral and yellow blend flower Salvias, especially Mexican Bush Sage,"Black and Blue" Salvia, and "Victoria" Salvia for their intense blue to almost purple color.
Many annuals are easy to grow from seed and actually perform better if they are seeded in the garden. Most commercial growers use a light potting mix so that plants flush out quickly. Once transplanted to the garden bed where soils (even good garden soils) are much heavier, they struggle to keep moisture in the original light soil used by the grower. Options include:
Zinnia, Celosia, Impatiens (mostly shade), Gomphrena, Vinca, Cosmos, Penta and Begonias.
All are grown in a dizzying array of summer colors. If you are using a mix of plants, it's best to choose one color of each variety and stick with it. In doing so, you compliment your color scheme rather than confusing it. However, planting a variety of colors using only one of the above annuals for the whole garden provides a tapestry of colors that play off each other instead of playing against other bloomers.