Not as green as cabbage looking

A phrase used by someone recently was

"not as green as cabbage looking"

Anyone know the origin (or even the meaning) of this please

'I'm not as green as I'm cabbagey looking' means 'I'm not as stupid as I might look.' A related expression, meaning much the same thing is 'I didn't come down with the last shower of cabbages.' 'Fraid I don't know the origins.

It sounds Southern to me but I haven't found it in a reference yet.

It sound very Irish to me.