punch of color suggestion

Hi, I am redoing a large flower bed at church. It is the largest, and is pretty much centered in the parking lot in line with the church doors, so I want it to to be the centerpiece that says Wow, come on in. I've started with a zigzaged row of red knockout rose bushes that point toward the door and i want to mirror each side since it is viewed from both sides as you enter the parking lot. Around the edge I've planted bright yellow mums for fall, and I'm planning other yellow blooming flowers for next spring.

I'm worried about the lack of height, and I'm wondering if I should add something taller in a small amount, and perhaps a bright spot of another color.

Any suggestions would be greatly appreciated.