Hello Harald,

in Addition to my last comment:
The 12. color was not defined because the place for it is used in the popup menu for the palette symbol/open dialog-button.
But in dialog mode we can use the proposed 12. defined color (or more lines too).
Therefore it has to be defined, as proposed.
To get *NO* new line in popup-mode, a second change is needed, just after combine the base- and user-colors together -> line 110:
    set colors [concat $_baseColors $_userColors]
++++
    # remove last user color to get space for palette button to open dialog
    set colors [lreplace $colors end end]
====
Then the rest goes right from -> line 111:
    foreach color $colors {

This solution is fine for more lines of user colors too.
That's all! Please do the change and commit it.

Thank You and best greetings
Thomas W.