Fix for U4-5145

Changes to not reset the color each time a color is added (keep the last
added color). Preferable if e.g. you want to add some colors close to
each other in the color spectrum.
If there is a reason to reset the color to default color (black) after
adding each color, the spectrum color picker should also change color -
then enable line 71 + 73-74 which use the set method.