[css3-background][Editorial] background-color computed value

From [1]: 

> Computed value: the computed color(s)

Why ”color(s)” instead of “color”, since background-color only accepts one color?

[1]: http://www.w3.org/TR/css3-background/#the-background-color

Lea Verou
W3C developer relations
http://w3.org/people/all#lea ✿ http://lea.verou.me ✿ @leaverou