What does dull eardrum mean?

Depends: A dull or absent light reflex from the eardrum may be a sign of a middle ear infection or fluid. The eardrum may be red and bulging if there is an infection. Amber liquid or bubbles behind the eardrum are often seen if fluid collects in the middle ear. So basically, the appearance of the eardrum must correlate with other signs and symptoms. See ENT doc for best advice.