Pigmentation on the legs can be due to a number of causes. Following eczema, the pigmentation is most likely post-inflammatory hyperpigmentation. This usually fades with time but may take weeks to months to clear. Some lightening creams may be prescribed to help this lighten faster. The benefits from laser for this condition though is less predictable.
You did mention that your pigmentation has been there for years, so other causes of lower leg pigmentation including pigmented purpuric dermatosis, stasis dermatitis and lentigines should be considered. So it may be advisable for you to see a dermatologist/doctor to confirm the diagnosis and advice on management.
