in city of ashes when magnus had custody of jace the hari clary came over was magnus wearing a green dress??

No it doesn’t say that Magnus was wearing a green dress, but a green dressing gaun (though it wouldn’t surprise me :D) “Magnus swept towards them. He was wearing a floor-length green silk dressing gaun over a silver mesh baju and black jeans.” (pge 129 of the City of Ashes)