Follow up with your dermatologist.
The suggestion to use sun screen is a sound one. However, this could just be post inflammatory hyper pigmentation. Often this will get better with sufficient time. Let the dermatologist evaluate your concerns and see what is recommended for your particular situation.
Patience & avoid sun exposure
It can be normal to have this response which may settle b/w 6-12 weeks after initial treatment.
Protect the eyelid skin from the sun & use a good SPF & sun glasses which are both UV A & B protective.
Discuss your concerns with your dermatologist.