You can colorize a black-and-white photo in one step by uploading it from dotphoto to the Photomyne color app:

At Photomyne, scroll down to Upload a photo and tap the button:

At dotphoto, click on your photo, and then tap the Share icon in the upper left.

Tap the green button to copy the link for the current photo:

In Photomyne, paste the link into the file name (Ctrl-V), and tap the Open key. This will open the dotphoto image in the colorize app.

Tap the Colorize photo button.

Save the colorized photo, and upload it to dotphoto. Here is a sample: