All of a sudden the veins in my thigh are really dark and all up and down my leg and i just had plantar faciitis surgery?

Get it checked out: Without seeing or examining your leg it's impossible to tell. One concern would be a deep clot in a vein that's called a deep vein thrombosis (dvt). This can be a complication of surgery as well as decreased activity. A DVT can lead to a more serious complication called a pulmonary embolus (pe). If untreated it can also lead to vein problems like varicose veins.You should get it checked out asap.

New onset leg veins.: If you have new veins forming on your legs then you should see a vein specialist for a full venous evaluation. Sometimes a venous duplex ultrasound may be necessary depending on the types of veins involved.