This works, but sadly there are better and cheaper options.
Ok so I tested this out with about 520 images, I was greatly disappointed by the fact there was no batch processing and that I had to wait between each image to click the next one... It took over 3 hours to complete... The final results were nice though, but then I discovered that I owned PixageFX on Steam... Which apparently has just gotten a colorized option, not only can it do still images with no limitations, but it can also process video and do batch processing. In about 90 seconds I had all my images processed and the results were about the same. The only thing I really noticed was that the blue light from the windows was a bit cleaner with the imagecolorizer than was Pixage, but that then we bring cost into the equation.
PixageFX costs $19.99 full features. It does more than just image colorization too, it has a ton of very specific filters including normal map generation to add 3 dimensional lighting effects to 2 dimensional images, pixelization dither effect that doesn't suck. Image repair, image vectorizations, AI based resize... I mean... It does a lot for just $20 and does it well and it much faster. Knowing this exists, I cannot recogmend imagecolorizer at it's current price. It just doesn't make sense.