color_chooser.py

#!/usr/bin/env python3

import sys

import gi
gi.require_version('Gtk', '3.0')

from gi.repository import Gtk

class Application(Gtk.Application):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.window = None

    def do_startup(self):
        Gtk.Application.do_startup(self)

    def do_activate(self):
        Gtk.Application.do_activate(self)

        if not self.window:
            self.window = Window(application=self)

        self.window.show_all()
        self.window.present()

class Window(Gtk.ApplicationWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        color_chooser = Gtk.ColorChooserWidget(show_editor=True, use_alpha=False)
        color_chooser.connect('color-activated', self._on_color_activated)

        self.add(color_chooser)

    def _on_color_activated(self, *args):
        colors = ', '.join([str(elem) for elem in args[0].get_rgba()])
        print('activated with rgba(' + colors + ')')

if __name__ == '__main__':
    app = Application()
    app.run(sys.argv)