Not a bad idea, depending on the UI, I wanted to do the same (a bit like scamadviser.com) but I think you should make no difference between yellow and red.
Keep it simple:
- Red: Not safe because <phishing link, proven scam, turned rogue...> (and why not a link source)
- Green: Safe service
- Grey: unknow service

Another thing that can be done to fill the database:
If the legit service is 1234.com, you can consider all othes TLDs not safe to use, and add them directly to the DB. It can save some time in the long run