Darkish-coloured pan Lady Jane possibly used? (5-4)

'darkish-coloured' is the definition.
(slate-grey is a shade of grey)

'pan lady jane possibly used?' is the wordplay.
I cannot really see how this works, but
'pan' could be 'slate' (both can mean to criticise) and 'slate' is found in the answer.
'lady' could be 'rey' and 'rey' is present in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).