At first artist questions using another shade of blue (4)
I believe the answer is:
aqua
'shade of blue' is the definition.
(I've seen this in another clue)
'at first artist questions using another' is the wordplay.
'at first' says to take the initial letters.
The first letters of 'artist questions using another' is 'AQUA'.
(Other definitions for aqua that I've seen before include "- Regia; - fortis" , "Blue tinged with green" , "Light bluish-green -- water" , "-- fortis, 'strong water'" , "Prefix denoting "water"" .)