Whole foot and ankle are purple after bad ankle sprain, is that safe/normal?

Can be. A sprained ankle means that you have torn some or a lll of the ligaments holding ankle together. This can cause bleeding shows up as a bruise. Depending on how much bleeding there is after the injury can cause the foot to turn purple initially. It may look bad but if you can still feel it when you touch your foot and the foot is warm to touch it is normal. If not see a doc immediately to check.
Ankle sprain. There is not a direct relation between the amount of "black and blue" and the degree of damage. Use rest ice elevate and compression bandage until you can get it checked. A bad ankle sprain needs to be treated correctly otherwise and unstable joint can develop.
NORMAL BUT... If it's bad, as you say, bruising is part of the process. But, the question remains, did you do damage to ligaments, or even break a bone? 40% of TREATED ankle sprains continue to have lingering problems. See a podiatrist. Sincerely, Dr. Latva.
Yes and no. You can definitely have a ankle "sprain" that is severe enough to cause pretty extensive swelling and bruising in the ankle and foot, but if you are experiencing these symptoms you would want to be seen, examined, and have X-rays to make sure you do not have a fracture.
Not Normal. Significant bruising can be indicative of torn ligaments or tendons. Possibly a fractured (broken) bone. Have x-rays done and see a podiatrist.
Sprain. The discoloration is normal. With that much bruising it should be evaluated. See your podiatrist.