Dog rolled over in bed, kind of blue (6)
I believe the answer is:
cobalt
'kind of blue' is the definition.
(I've seen this before)
'dog rolled over in bed' is the wordplay.
'dog' becomes 'lab' (short for labrador).
'rolled over' says the letters should be written in reverse.
'in' indicates putting letters inside.
'bed' becomes 'cot' (cot is a type of bed).
'lab' back-to-front is 'bal'.
'bal' put within 'cot' is 'COBALT'.
(Other definitions for cobalt that I've seen before include "Metal element" , "Silvery-white metal used in alloys" , "Metallic element used in blue/green pigments" , "Hard ferromagnetic element, Co" , "kind of blue" .)