Ghostly: just like the light coming from a prism? (8)
I believe the answer is:
spectral
I believe this is a double definition.
'ghostly' is the first definition.
(synonyms)
'just like the light coming from a prism?' is the second definition.
(a prism shows the spectrum of visible light)
(Other definitions for spectral that I've seen before include "covering a range of colours" , "Like a colourful band" , "Ghostly; of bands of colour" , "Rap Celts for being ghostly" , "Ghastly" .)