Credit: Darrow Montgomery

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If you see some yellow on a Capital Bikeshare seat today, don’t be alarmed: It’s all part of the program.

To celebrate its 400th station in the D.C. region, Capital Bikeshare has placed 100 yellow (and red) seat covers designed by New York-based company CitySeat on 100 bikes throughout the system today. (Riders who post photos of their “scavenger hunt” experience on social media will be entered to win one of 10 annual bikeshare membership gift certificates.) The latest station lies the farthest east of the Anacostia River, near Division Avenue and Foote Street NE in Ward 7, and a block south of Nannie Helen Burroughs Avenue NE. It brings the total count of docks in Wards 7 and 8 to roughly two dozen. In October, the District Department of Transportation proposed adding nearly 100 new bikeshare stations by fiscal year 2018.

Lucky riders have started posting smiley September self-portraits selfies on Twitter and Instagram:

Sept. 20 marks the sixth anniversary of Capital Bikeshare.