In the summer I attend some summer training. In one of the training we did some science experiments. We used a coffee filter and a vis a vis marker (black). We did dots on the filter. We made a hole in the middle and inserted a brown paper towel that was dipped in water. As the water was being absorbed by the paper into the filter you would see the true color of black. This experiment only works with black vis a vis markers. Students will love to see how black is really made. Have fun!