At the present time, there is no need to have special skills for this. It is enough to know the desired service and be able to use it.
Colorize is a service based on machine learning, which colors the photo with color shades.
Moreover, it colors not with a random set of colors, but analyzes the image and selects the appropriate colors. For example: the sky is blue, the grass is green, etc.
The service requires mandatory registration, and without purchasing a paid subscription, it places a watermark on the photo “Created by colorize.cc“.
But the site displays a comparison image after clicking on the button on the right under the photo, in which the watermark is present only on the black and white image.
This way you can save the image and cut out a color photo without a watermark in a photo editor.