Constipation in the first trimester is so common and many of us went through the same thing, so you are definitely not alone. The green colour can sometimes be linked to prenatal vitamins or changes in what you are eating, which is pretty normal during pregnancy. That said, since you are 8 weeks along, it would be good to just mention both things to your gynae or doctor at your next visit, just so they can check and put your mind at ease. Staying hydrated and eating more fibre helped me a lot during that stage, so maybe give that a try in the meantime.