Rainbows particles dispersed, except one (8)
I believe the answer is:
spectral
'dispersed except one' is the definition.
I can't tell whether this defines the answer.
'rainbows particles' is the wordplay.
'rainbows' becomes 'spectra' (I've seen this in another clue).
'particles' becomes 'l' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'spectra'+'l'='SPECTRAL'
Can you help me to learn more?
(Other definitions for spectral that I've seen before include "covering a range of colours" , "Ghostly; of bands of colour" , "Spooky" , "Ghastly" , "Of or like a ghost" .)