Dull one might say “welcome” (3)
I believe the answer is:
This clue is a double definition.
'dull' is the first definition.
(mat as opposed to glossy)
'one might say welcome' is the second definition.
(as in a welcome mat)
(Other definitions for mat that I've seen before include "Foot-wiper on which welcome may be kept" , "What the cat sat on?" , "Small carpet" , "Rug; without a shine" , "Rough piece of floor-covering" .)