You are correct that poor circulation can cause both conditions, although it's also possible that your numbness and nail discoloration are not related.

CNN: Does my numb leg mean I have a circulation problem?

Poor circulation has a number of potential causes, including blocked arteries, varicose veins, liver or kidney disease, extreme cold, or as a side effect of certain drugs or medications.

CNN: Does my numb leg mean I have a circulation problem?

Oswell said wearing flip-flops can be seriously detrimental for people whose feet are already at risk: For people with diabetes, who often have poor circulation and feeling in their feet, wearing flip-flops can expose them not only to injury but to infection.

CNN: Flip-flops present feet with a painful problem

Poor water circulation meant that the organic material was covered before it could decompose, and it was eventually transformed into oil and natural gas.

FORBES: Going deep