Brown smear concealed excellent array of colour (7)
I believe the answer is:
rainbow
'array of colour' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'brown smear concealed excellent' is the wordplay.
'smear' indicates anagramming the letters (I've seen 'smeared' mean this).
'concealed' is an insertion indicator.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'brown' with letters rearranged gives 'rnbow'.
'rnbow' going around 'ai' is 'RAINBOW'.
Can you help me to learn more?
(Other definitions for rainbow that I've seen before include "Arc of colour in the sky" , "colours in the sky" , "'The - - ' by D H Lawrence novel" , "There's a pot of gold at the end of it" , "'I can sing a - - ' (song)" .)