Don't use `sun-flower` for helm foreground

`sun-flower` is used for the `helm-selection` face background, so none
of the helm foregrounds should use the same color. Otherwise we end up
with yellow-on-yellow and the text is unreadable.

Fixes #4

@john2x I randomly picked `asbestos` for this, but it could easily be any other color, I'm happy to change it if you have another pick.