Character vector, indicating the colour for printing.
May be one of "white", "black", "red", "yellow", "green", "blue",
"violet", "cyan" or "grey". Bright variants of colors are available
by adding the prefix "b" (or "br_" or "bright_"), e.g. "bred" (or
"br_red" resp. "bright_red"). Background colors can be set by adding
the prefix "bg_" (e.g. "bg_red"). Formatting is also possible with "bold"
or "italic".