I have used full strength peroxide to great effect. I would test your yellow and blue fabrics first, because the peroxide is sure to wick to those adjacent squares no matter how lightly you apply the peroxide. For my quilt, the peroxide didn't bleach any of the adjacent colored fabrics and the marker came out completely. You can Google HP as stain remover and see recommendations for adding a little dawn and/or baking soda, but in my case I didn't do that. I just used it full strength, completely saturated the markings, and then waited for the stains to fade and disappear (took about an hour) after which I plunged that part of the quilt in water to dilute the HP. Stain was gone and the adjacent fabrics none the worse for the experimentation. Good luck.
PS--I hear stain removal is more easily accomplished if you have pre-washed your fabrics.