When the user is changing the colors in either the ColorPalette ( using mouse press drag operation) or Custom Colors dialog - the preview rect reflects these changes. Instead it should reflect the newly selected color ( if there is one) or go back to the previous selection if the operation was canceled.
For ColorPalette - that would be if user press + drag and released outside the grid. ( preview does not change).
For CustomColorDialog - clicking on cancel. if Use or save is clicked, then the color in preview will change to the newly selected color as depicted in the new color rectangle.