In many parts of the world, the rocks are covered by grass, trees, farmland, buildings, parking lots, etc. They can make if very difficult to find out what is under the surface. In those areas, road cuts are a great way to see the rocks that are normally hidden. They can reveal different layers of rock, faults, igneous intrusions, and many other geologic structures that are normally difficult to see.
One of the fun parts of geology is learning to read rocks. I don't mean reading words that people have painted or carved on them. Instead, I mean examining the rocks, looking at their minerals, structures, position, fossils, and other things to discover what they can tell us about the history of the Earth.
In the Minerals unit, we learned that color is not usually reliable for identifying minerals. While it is not a good way to identify minerals, thanks to the melting points of different minerals, it can be useful for identifying igneous rocks.
Remember that igneous rocks form from magma, and not all magmas are the same. Some are hotter (more than 1300°C/2400°F), and some are cooler (as low as 700°C/1300°F). Because different minerals melt at different temperatures, hot magmas are usually very different chemically from cooler magmas.