If the skin on your feet seems smooth and normal, aside from just being red, then it may be a circulation problem. This may particularly be the case if your feet are red when you are sitting down or standing up, and then when you raise your feet, they return to normal color or become just a blotchy red. If that is the case, it points to the redness being due to pooling of the blood in your feet with gravity.
Even if the pulses in your feet (there’s one on the top of the foot and one by the inner ankle bone) feel strong when your doctor examines them, you can still have circulation problems in the small blood vessels of the feet. A way to evaluate for that is to get a special test in which they measure blood pressure in your ankles and in your toes. You might ask your doctor about getting that test (which is usually done in a hospital vascular lab).