You can do it yourself as the color scale is customisable.
https://www.windy.com/colors?rain,45.368,2.329,5,i:pressure
Select overlay -> Rain . You just need to modify the first line of Rain color settings as shown in this article:
https://community.windy.com/topic/10336/customize-the-color-scales-of-windy-layers?_=1667371914020
I am not sure that a bluish background would be a good idea as rain is displayed in blue.
