Clove pinks and creeping phlox would give you some summer color in the palette you like (I'm the same way...I like pastels best). This summer I actually went ahead and put in a small bed of annual calendula with a deep red dahlia in the middle and I couldn't believe how much I liked it.
I'm very taken with Geraniums too, and they pair well with catmint (I have Walker's Low growing in mats all over the place. I like the way the silvery leaves and soft blue flowers blend with just about anything...put it next to pink and the pink glows, put in next to yellow and pops.) Iris and peonies leap to mind, altho they won't get you too far along into the summer.
Thats one of my biggest challenges...trying to get some color into the mid-late summer garden. Most of the things I love best are early/mid summer bloomers.
I'll keep thinking!
Annie
