dishwater
as dull as dishwater

ditchwater
dull as ditchwater

dull
dull finish

Dull-blue Flycatcher
Eumyias sordidus

dull-browed
com cara pouco expressiva

Dull-colored Grassquit
Asemospiza obscura

Dull-mantled Antbird
Sipia laemosticta

dull-witted
de raciocínio lento

work
...Jack a dull boy