Should I be concerned if I have green vaginal discharge?

Yes. Women know their bodies and might be familiar with many types of vaginal discharge. However, an unusual one or a new one should be evaluated by a professional. If yellowish green, it could be trichomonas, which an obgyn provider should diagnose and treat. If the woman is pregnant and the discharge is darker green, it could be meconium-stained amniotic fluid, and that could become an OB emergency.
Yes. Greenish vaginal discharge is frequently associated with the trichomonas parasite which can be identified under the microscope as moving flagellated parasites. Since there could be other causes you need to see a gynecologist for an examination, and a wet mount examination of the vaginal discharge.
No. Discharge color depends on the predominant bacteria in your vagina, but it also can be affected by what you eat.
No. The color of vaginal discharge can vary. The foods you eat, the vitamins you take can affect it. You should get checked for STDs if that is an issue.