Implantation bleeding

Guys can I have 4 questions regarding implantation bleeding.

1. Implantation bleeding can occur before or after 3 days of period due or not

2. How to differentiate implantation bleeding and mensural bleeding. Because I had periods late for 3 days and today I got bleeding with mild cramps.

3. There is any colour difference or days to differentiate it.

4. I will get my regular mensural cycle for 1-3 days. So how to differentiate mensural cycle and implantation bleeding.