Sequence observed in perfect rainbow (5)
I believe the answer is:
train
'sequence observed in perfect rainbow' is the definition.
'train' can be an answer for 'sequence' (thesaurus). I'm not certain of the 'observed in perfect rainbow' bit.
'in perfect rainbow' is the wordplay.
'in' indicates a hidden word.
'TRAIN' can be found hidden inside 'perfect rainbow'.
Can you help me to learn more?
(Other definitions for train that I've seen before include "School - transport" , "Number of eg carriages in a line" , "Body of followers, retinue" , "Linked carriages" , "Choo-choo or part of wedding dress" .)