Streak is the color when you scrape the mineral across a white or black porcelain tile. The color that you get is the powdered color of that mineral. It does not matter what the actaul color of the mineral is because the streak color can be completly different.
Color is the apperance of the mineral. When indentifing a mineral, color is a great thing to know but I would not rely on it. The reason you should not rely on the color is because some minerals can be many different colors. For example, the images below of florite, you can see that they are orange and purple. However, florite can also be white, black, clear, colorless, red, blue, pink, brown, green, and yellow. Color is a great property to get you started but not one to rely on.