name1: color1
name2: color2
... Color names must be acceptable as identifiers in the [gtkrc][gtk3-Resource-Files] syntax, and color specifications must be in the format accepted by [gdk.color.Color.parse].Note that due to the way the color tables from different sources are merged, color specifications will be converted to hexadecimal form when getting this property.
Starting with GTK+ 2.12, the entries can alternatively be separated by ';' instead of newlines:
name1: color1; name2: color2; ...