Map markers always have white symbols or labels. If a light background like yellow is used this could not be read easily. In case of light backgrounds black labels should be used.
This task was mentioned at Community-Wishlist-Survey-2017 (https://meta.wikimedia.org/wiki/2017_Community_Wishlist_Survey/Miscellaneous/Kartographer_improvements), which got the No.1 out of 214 proposals.