What may parody some pinto mares (source of humour?) (9,6)

'humour?' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'what may parody some pinto mares source of' is the wordplay.
I cannot quite understand how this works, but
'what' could be 'eh' (sound used to ask 'what?' or 'pardon?') and 'eh' is found in the answer.
'some' could be 'a' and 'a' is found in the answer.
'of' could be 'o' and 'o' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?