Who write the mysterious letter? 

It was a rainy day. In the Anna´s school locker there was a  mysterious letter. One unknown classmate left there this message:

You have five marker from Anna´s classmate. Find out, who was the unknovn friend?

Several markers are used to put colored dots on the line. The paper is then dipped in a water in a cup, with the water level below the dots. Capillary forces draw the water up through the paper. The inks dissolve and travel up with water, in the process separating into constituent pigments.