Of course, as explained by the link I provided to you, you must modify the color scale on the website windy.com i.e. on a desktop. Then your modifications will be applied automatically to your phone app.
Windy offers you the possibility to modify the colors exactly as you wish by yourself. If you want a range of colors for the wind based only on shades of grey, you can. But do you think that if windy changed this color scale to a shade of grey it would please all the users of this application?
So do it yourself!
Personally I prefer the world in colors.