Fix #83: custom color in Tk/QTk
Fix #83: custom color in Tk/QTk

'#' is the virtual concatenation of 0 virtual strings,
and hence represents the empty virtual string.

"#" is a virtual string with one character, #.
eregon/mozart-graal,eregon/mozart-graal,mistasse/mozart-graal,mistasse/mozart-graal,eregon/mozart-graal,eregon/mozart-graal,eregon/mozart-graal,mistasse/mozart-graal,mistasse/mozart-graal,mistasse/mozart-graal,eregon/mozart-graal