Diamonds, yellowish-white, 99 maybe (3,5)
I believe the answer is:
ice cream
'99 maybe' is the definition.
I can't judge whether this defines the answer.
'diamonds yellowish-white' is the wordplay.
'diamonds' becomes 'ice' (slang term for diamonds).
'yellowish-white' becomes 'cream' (yellowish-white colour).
'ice'+'cream'='ICE-CREAM'
Can you help me to learn more?
(Other definitions for ice cream that I've seen before include "dessert will appear" , "Frozen desert" , "Eric came to get confection" , "Party food" , "Cool summer confection" .)