The dark spots on the legs,thigh might be from different cause than usually we get on face and arms. Could be just due to UV light or other systemic cause. So it is better to consult a dermatologist to evaluate the spot. Normally non raised black spots can be faded with creams but if your black spots are raised then treatment has a different approach than creams. There are many options for treatment including Lasers, skin lightening peels and so so depending on the type of spot.
You can check our Skin Pigmentation forum for more tips and suggestions:
http://dermatalk.com/forumdisplay.php?f=14