In a color class in preschool, children can learn a variety of things related to colors. Here are some possible things that could be covered:

1. Basic colors: Children should learn the basic colors such as red, blue, green, yellow, orange, purple, black, and white.

2. Color recognition: Children should be able to recognize colors by name and by sight.

3. Color mixing: Children can learn how to mix primary colors to make secondary colors.

4. Color patterns: Children can learn how to create color patterns, such as red-blue-red-blue, or red-yellow-blue-red-yellow-blue.

5. Color sorting: Children can learn how to sort objects by color, such as sorting red blocks from blue blocks.

6. Color identification in the environment: Children can learn to identify colors in their environment, such as green leaves or a blue sky.

7. Color matching: Children can learn how to match colors, such as matching a red toy car to a red block.

Overall, the goal of a color class in preschool is to introduce children to colors and help them develop an understanding and appreciation of the role that colors play in our world.