Megan-Shape and Color

Megan ability to recognize shape and color improved a lot. Now she can do the shape puzzles all by herself (with a lot of encouragement and cheering of cause)

But I don't know why, she can pair the color (that mean she isn't color blind) but she can't name the difference between each colors such this is red or blue or yellow. But she knows half of red circle must pair with another half of red and so does the other color of shapes.

Wonder why? How to teach 2 years old color? Kindly share, please....