Edit hex color stamps using a QT, or the internal color picker.
This mode can edit any color representation rainbow-mode can recognize. A limitation being that it will always write in #FFFFFF format.
Go to the qt_color_picker directory
$ qmake qt_color_picker.pro
$ make
Move the resulting qt_color_picker file somewher in you path. Alternatively change the value of es-color-qt-picker-exec to the location of the executable.