Diamond perhaps with slight, not light, colour (5)
I believe the answer is:
stone
'diamond perhaps' is the definition.
(diamond is an example)
'light colour' is the wordplay.
'light' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'colour' becomes 'tone' (tone is a kind of colour).
's'+'tone'='STONE'
'with slight not' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stone that I've seen before include "Gem; Staffs. town" , "Little rock" , "Boulder" , "Pebble" , "14 lb" .)