Why? there beautiful monochromatic plants to compliment what you have.
I'm having a hard time doing a URL link (paste)

Google...Chocolate Flower Farm

Jim

I once designed a totally brown garden, brown & buff with mirrors as a Daguerreotype garden. The photos we had when I was growing up had all faded to buff and browns, and I loved them! These flowers would fit right in! I like them!!

I dunno, I think I'd dry those and use them for fall decorations! They would be spectacular with some of those dwarf mexican sunflowers (I think that's what they are called? Anyhow they bloom a little earlier than regular sunflowers). Don't know if that helps at all for your kit kat garden though! lol*

There are some brownish daylilies that would fit right in with your rudbeckias: 'Duke of Durham' 'Fires of Fuji' 'Jambalaya' 'Milk Chocolate' 'Savannah Art' 'Honey Glazed' 'Tennessee Tan' 'Double Almond' -- just to name a few.

'Queen of Night' tulips have a beautiful brown sheen to them. 'Eye of the Tiger' Dutch Iris have brown falls and then some really pretty German Iris in brown shown in this forum this past spring.

Then in fall, all those bronzy color Mums.

I have quite a few brown flowers......they just did not start out that color.
I have chocolate mint, which smells like chocolate.
You could add cocoa mulch, they say it smells like cocoa.

There is a chocolate cosmos, too.

Although some have problems with it self seeding I have Anthriscus sylvestris, lovely chocolate colored foliage. I cut the flower heads off before they go to seed so I don't have a problem.
Another I don't have but have seen pix of is Delphinium 'Kissed by Chocolate' looks kind of interesting.

Annette

-Tom, if you do a quick search on this forum you will find some old threads about 'Chocolate' flowers. One has pics I think. There was also one on the Perennial Forum a while back that had a really great long list of plants.

There is a chocolate basil too I think. And it might be fun to grow a 'Chocolate Cherry' tomato in the bed or in a pot nearby. Don't forget Eupatorium 'Chocolate'.

Berlandiera lyrata is a Rudbeckia like flower that has a strong Chocolate scent (I don't grow it myself).

There are also a collection of "coffee roses" that have tan colors and (to my eye) brownish tints that might fit into your scheme. Rosa "Hot Chocolate" for instance. Here is a great article on coffee roses:
http://www.rdrop.com/~paul/main11.10.00.html

I can think of a few more 'Chocolate' flowers, but I don't think they would grow in your zone (can you grow Columbine??)
CMK

Here is a link that might be useful: Berlandiera lyrata

Any ornamental grasses that would suit you?

CMK, I already have a chocolate Joe Pye weed. Unfortunately, it's purple, not brown.

Yes, my columbines are getting huge.

I have a few grasses already too. I'm thinking of just making it a simple rudbeckia bed with some shastas in there for variation.

Sounds like an interesting project!

Years ago I had a chocolate mint plant. No colored flowers but a nice choco-mint scent.

Not sure how any of these are in your zone but here are some brown/brown flowering plants: Terra Nostra roses, callas, chocolate cosmos, hypericum berries, fiddlehead ferns, gerberas, Dahlia 'Arabian Night'.

A blog I follow mentioned the Chocolate Farm today.

Here is a link that might be useful: Chocolate Flowers

Ok, just reread and looked up some suggestions. There's a lot more brown out there than I thought. I have a bearded iris from my sister that's brown and yellow. I think I even had one of my own bloom this spring. There's daffodils for spring. I've given up on tulips forever. Some larkspur, columbines, and into the summer with rudbeckias taking the main stage. Cosmos poking out between the Brown eye Susans. A few sparse orange daylilies bobbing in the background. By fall, crocosmia blooming against the red flame maples in the gully. From buttery yellow to crisp and burnt.

Bronze carex, carmel heuchera,

several foxgloves are brown too, like the digitalis lantana, and d.ferruginea. I grew them from seeds since they're harder to find in nurseries. i also like my toffee nose poker a lot and my toffee twist carex. yolana

Big foliage: species cannas with bronze leaves. When they finally bloom, the blossoms are red and small. Planted in shade, they never bloom, just great foliage.

The bracts on 'red' shrimp plant are shades of brown rather than a true red. Where mine died back in last winter's cold, they've grown back in nice little shrublets with many blooms. Good hummingbird plant, too.

Nell