Read this passage from "Types of Volcanoes" and then look at the image. Volcanoes are structures formed around openings (vents) in the ground where molten lava, ash, or gas escape from inside the Earth. We have all heard of lava, but not everyone knows how it forms. Deep inside the Earth, rock that melted long ago beneath the Earth's crust forms magma, a very hot liquid that mixes with dissolved gases and crystals. When this magma flows up above Earth's surface, it is called lava.

A cross sectional view of a volcano erupting, showing red lava underground and fading to orange as it reaches the top of the volcano.

The color in the center of the diagram most likely changes from red to orange to

show the difference between the formation of magma and lava.
help grab the viewer’s attention with more than a single color.
give a warning with the color red that volcanoes are dangerous.
show how the temperature of magma changes as it rises.