There is no bug here !
The white or magenta animated particles have nothing to do with the wind color scale. The white or magenta colors are just chosen to get a good contrast with the map.
The colors of the map give the wind speed accordingly to the colors of this scale, not the animated particles which only give the direction of wind.
So there is nothing to fix.
Right there is no way to customize the color scale on the App. You have to do it on the websitewww.windy.com, on desktop/laptop.
On iPad it is possible if you use your browser with www.windy.com
See screenshot of my iPad with color scale settings page