Art form involved with origins of the underworld and source of rainbows? (5,4)
I believe the answer is:
trout farm
'source of rainbows?' is the definition.
(rainbow trout is a type of trout)
'art form involved with origins of the underworld' is the wordplay.
'involved with' is an anagram indicator (involved can mean confusing or complex).
'origins of' indicates taking the first letters.
The initial letters of 'the underworld' is 'tu'.
'art'+'form'='artform'
'artform' with its letters anagrammed with 'tu' makes 'TROUT FARM'.
'and' is the link.
(Other definitions for trout farm that I've seen before include "Where fish are bred" , "fishy business" , "Commercial fish producer" , "river factory" , "place of rainbow?" .)