The Art League
The Art League, founded in 1954, is a charitable and educational nonprofit organization devoted to promoting and maintaining high standards of fine art in the Washington D.C. area. The Art League seeks to stimulate and encourage artists by operating a gallery with many opportunities for members, including monthly juried shows of members' work, other chances for exhibition of work and many educational possibilities. The League is a multifaceted visual arts organization that meets its mission through its gallery, fine art school, and arts-outreach programs.
I like the White Galaxy Marker very much for writing on dark paper, and I have used it to cover another color when I needed to disguise a mistake or simply change effect.
For example, I bought an ornament with name SCARLETT spelled on it and by covering the last 't', I was able to give this to someone with a cat named SCARLET.
If color to be covered is a paint or other pen color, that can make the other color "stain" the white marker tip. This can be avoided if one is sure first color is dry before trying to cover it with white.