A neutral decor lends itself to many flower colors, including the brightest shades of midsummer. There is one reason some flowers, such as marigolds, snapdragons, cosmos, black-eyed Susans and sunflowers, are planted so often by so many people. They grow and they produce. That's what you want in your cutting garden. Don't forget foliage.
Foliage is an important part of any arrangement.
But you don't have to devote part of your cutting garden to foliage. You can snip stems here and there from your evergreens to tuck into the arrangement. Hardy ferns grow beautifully, usually in shady areas. Don't be afraid to cut them.