Yellow DOS 2.5?

Way back in the day, a friend gave me a disk that had some weird version of Atari DOS 2.5 on it.  He called it "yellowdos" or somesuch.  I've attached a screenshot.  I guess it looks kinda yellow.

I haven't been able to find any reference to this DOS anywhere.  It doesn't look like it's in the Atari 8-bit FAQ.

I did find a DOS 2.8F with modifications by E.T. Horst which has a yellow DUP screen, but it's not the same.  It can be found at: http://www.mixinc.net/atari/download_a8/dosdisk.htm

Any ideas where this yellow Atari DOS 2.5 came from?

Thanks!

-Joe