Did you know?

A yellow person is someone who who shows fear or timidity.

He's yellow! [coll.] = Er hat Schiss! Er ist feig.

Why does calling someone "yellow" mean cowardly? Before the United States'Civil War, there were two opposing sides on the issue of slavery. As the debates between these two groups continued, agitators on both sides published anonymous pamphlets and flyers which attacked public figures.
These unsigned publications, which typically contained vicious lies and rumors, were usually printed on cheap, unbleached paper that had a yellow tint. When it was learned certain newspaper editors were contributing to the publishing effort, the practice became known as "yellow journalism."
Eventually, the term "yellow" became known as a cowardly act.

Here are some interesting synonyms which mean "yellow"

cowardly
chicken
chickenhearted
lily-livered
white-livered
yellow-bellied
cowering
cringing
craven
recreant
dastard
dastardly
faint
fainthearted
timid
poor-spirited
unmanly

A yellow person is also named a:

shrinking violet
sissy
pansy
waverer
vacillator
hesitator
hesitater


And finally, to make you a "yellow expert" here are the most common other uses of this colourful adjective:

yellow plum - die Mirabelle
Yellow Star - der Judenstern
yellow pages - das Branchenbuch
yellow boletus - der Steinpilz
yellow journal - das Revolverblatt
yellow of an egg - das Eigelb
yellow mica [min.] - das Narrengold
yellow fever [med.] - das Gelbfieber
yellow lines - gelb markierte Bordsteine (No Parking!)
yellow dog contract - (Am:) Arbeitsvertrag mit der Verpflichtung, keiner Gewerkschaft beizutreten