I have a purple spot on the bottom of my right foot. I have had it for years with no pain, should this be a cause for concern?

Have a doctor see it. When you are at your next doctor visit ask your doctor to tell you what it is. You need a diagnosis to know if it is anything that needs treatment.
Likely not. It would be good for you to consult your doctor at your next visit. From what you have described, it is a vascular malformation and not likely to cause you any trouble.
Probably OK. it is probably benign hemangioma . You can check it out with the dermatologist.
No pain, no change. Are all good signs! If it does not worsen it is likely nothing much, like freckles.. Do show your doctor so it can be monitored by both of you. If it does change in size or symptoms, check with your doc again.
Maybe. A purple "spot" can be harmless such as a hemangioma. However, one can't diagnose this without looking at it, Any change in the spots appearance,size, color or borders would warrant a closer examination to rule out skin cancer.