Hi maroulis
Add this to your map-style in ja google map plugin settings
[{"featureType":"water","elementType":"geometry","stylers":[{"color":"#000000"},{"lightness":17}]},{"featureType":"landscape","elementType":"geometry","stylers":[{"color":"#000000"},{"lightness":20}]},{"featureType":"road.highway","elementType":"geometry.fill","stylers":[{"color":"#000000"},{"lightness":17}]},{"featureType":"road.highway","elementType":"geometry.stroke","stylers":[{"color":"#000000"},{"lightness":29},{"weight":0.2}]},{"featureType":"road.arterial","elementType":"geometry","stylers":[{"color":"#000000"},{"lightness":18}]},{"featureType":"road.local","elementType":"geometry","stylers":[{"color":"#000000"},{"lightness":16}]},{"featureType":"poi","elementType":"geometry","stylers":[{"color":"#000000"},{"lightness":21}]},{"elementType":"labels.text.stroke","stylers":[{"visibility":"on"},{"color":"#000000"},{"lightness":16}]},{"elementType":"labels.text.fill","stylers":[{"saturation":36},{"color":"#000000"},{"lightness":40}]},{"elementType":"labels.icon","stylers":[{"visibility":"off"}]},{"featureType":"transit","elementType":"geometry","stylers":[{"color":"#000000"},{"lightness":19}]},{"featureType":"administrative","elementType":"geometry.fill","stylers":[{"color":"#000000"},{"lightness":20}]},{"featureType":"administrative","elementType":"geometry.stroke","stylers":[{"color":"#000000"},{"lightness":17},{"weight":1.2}]}]