get rid of duplicate code in parse_config_text by trying to parse the value as the variable first

[rexim]

introduce in #209

That will require somehow distinguishing the variable names and the color values.

The easiest way to do that is to introduce a prefix for color values. Usually it is #. For example #69696969.

But we already use # as the comment prefix. So we have to also choose a different comment prefix and migrate the

current config.var.