What Causes An Indentation On The Outside-top Of The Foot

what causes an indentation on the outside-top of the foot (about 3 inches long, 11/2 inches wide 1/2 deep with slight discoloration (darker pink) and no pain). It is about midway between ankle and toes. I have not suffered any type of incidents or trauma in weeks other than a stubbed toe. I am obese and recently told I was Diabetic But I have lowered my blood sugar last time I was seen, while still trying to eat better. .Also high blood pressure all medicines I am on have been unchanged in over 5 years> I hope that enough complimentary info