Source of colour in some light defined by study (6)
I believe the answer is:
This could be a double definition.
'source of colour' is the first definition.
(I've seen this before)
'some light defined by study' is the second definition.
'crayon' can be an answer for 'study' (thesaurus). I'm not certain of the 'some light defined by' bit.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for crayon that I've seen before include "drawer" , "One colours with this" , "Drawing-stick" , "Coloured rod" , "Coloured wax pencil" .)