Here is a great idea that comes to us from the docents who lead nature education programs at the Bouverie Preserve in Sonoma County. They use nature journals with some of the students who come through their program. They grind their own pigments by finding soft colored rocks in a stream, rub the rocks on a hard rock with a little bit of water and then add color to their journals. You could do this anywhere you go, adding a splash of real color from the landscape. If you have a paintbrush or waterbrush you can control the painted shapes easily. Even if you are not using the color to paint a part of a drawing, you could make a sidebar of color found in the landscape around you.
Pages of a student journal colored with paint make in the field by grinding rocks in a little bit of water.