I can personally attest to this! Once, ages ago, my parents took my brother and me to Washington D.C. in October. The weather was MUCH cooler than it would have been in August (hello, humidity) and the colors were absolutely incredible spread out through the Capital! While here you should, of course, visit all of the monuments possible and be sure to check out the Smithsonian, and if you can, drive the thirty minutes to Mount Vernon. It’s completely worth it!