Just for interest, this is the boa in American Samoa..
I discovered her dark colouration is indeed from her being gravid. I took her to my friend working at the hospital and we did an ultrasound and x-ray. You can see from the attached pic she is full of young! We caught her sometime in Nov. so she is at least 3 months along. Judging from the x-ray do you have a feel for how much longer she might have before birthing? Crazy.
Hope you are well and all the best!