Decorative Dahlias provide colour through to the first frost. This dahlia was snapped in the rain at Harrogate Valley Gardens which has a great show of Dahlias in their own raised bed. That may account for the six foot specimens that were on display.
I was taken with the two tone effect of this flower. Many of the other flowers at this time of year are the brash purples, striking pinks or strong yellows. Check now in parks and public place to see what colour schemes work. Then plan your own scheme for next year.