As from your history you are on treatment with tetracycline
for eye lid swelling.
Usually tetracycline is prescribed as a treatment for blepharitis
one of the reason for recurrent chalazion
Darkening of the eye lid skin is usually not caused because of tetracycline ointment application. However darkening of skin is known to occur in blepharitis because of chronic inflammation.
I advice you to consult your eye doctor for diagnosis and treatment accordingly.