I remember this when it was first online as a web app and it was a pretty big hit amongst Manga fans. I remember someone was finding the server costs but then they shut it down. I guess they had trouble monitizing it? I always wondered whether this could actually become a useful+profitable product.
This is also essentially built into Clip Studio. It’s usually not worth the effort. You have to spend a lot of time putting down color hints for it to do anything remotely good, and at that point you’re already basically laying in the painting anyway.
I'd say it depends on the original line art: for anime it seems to put mostly correct colors right from the get-go, saving some time for the basic coloring. But most other art styles, you have to do most of the work yourself, as you said
https://i.gyazo.com/474eab5c14ed592fc83a4a369ae675a8.png
https://i.gyazo.com/2b222788af78495f9c629347f8399e8f.png