Habsburg Flag

The Habsburg Flag consisted of two equal bands of black (top) and yellow, and was used in the Habsburg Empire. It's colors come from the Coat of Arms of the Holy Roman Empire: the golden field and the black, double-headed eagle.

The original form of this flag, introduced in 1686, featured a yellow background with the double-headed eagle. However, this proved to be a complicated design and was too hard to reproduce. From 1720 onward, the simpler form with the yellow and black bars started to appear. With the end of the Holy Roman Empire in 1804, this flag was approved for use as a civil flag. For naval and military uses, the newly founded Austrian Empire introduced the now-familiar red-white-red with the Austrian coat of arms.

References

http://www.flaggenlexikon.de/foest1.htm (German)