Basic map stuff - How colors are used

Years ago, in physical geography, we had to color in a physiographic map of the United States. I loved that activity, with colored pencils, and thin pens, and geology references. The teacher told us that we could choose our own colors, and one student showed him her map with the sea colored orange. He said, "I know I told you that you can choose your own colors . . . but just no. No. The sea cannot be orange." And he had her start over. It was sad, but . . . just no.