The author of this tutorial is Martine Raymond. He found it easy to add vivid color to this old family portrait with AKVIS Coloriage AI.
Note: The example was made in an old version of the program. From version 15.0, this method is available in the Classic mode.
To colorize such a dark, monochromatic photograph in bright colors, some preliminary color correction is needed. Use any of the correction methods in the Image -> Adjustment menu.