I’m using the built-in google map element and I cannot get the map to be a grey hue. I have tried using black as the color, white and any number of greys and it always reverts to red as the hue.
Please add -webkit-filter: grayscale(1); to the inline style of google map settings (See http://prnt.sc/79go5j ) instead. Black and white and all the pure shades of gray — do not indicate a hue.