Colored host names should be optional

[caoliver]

The coloring of hostnames by their hash should be optional. This bit of eye candy can make the names hard to read on certain background colors. While one can specify TERM=xterm-mono, that disables the highlighting of the sort column. In my particular case, I generally run a pale beige background, and the off-white color is nearly invisible. To be quite frank, I'm not really sure that coloring the hostnames conveys useful information at all.