Set the correct colorspace on the internal color selector
This adds a separate instance of the internal color selector for the background color selector, making sure that both fg and bg selectors are handled the same way.
It also removes locking the colorspace on the internal color selector: that was called only when setColorSpace was called on the dual color button, which only happens if we switch images in the view manager. Now it also sets the colorspace of the current node, not the image.