There is, as far as I know, no way to show the grid on top of all objects.You can however change the color in the Objects docker, just as with any other layer.Click the (grey) colored bar on the right hand side of the Grid layer in the docker, and select any color from the dialog that appears.
This overlay is a good command hence asking in a future update. user can notice every element horizontally and vertically alignment with other objects at once. By having beneath the objects there is no use of this. hence this option is very useful