Put the slider at the bottom and select R. Notice that with R = 0 only green and blue hues appear.
Now move the slider until R = 255 and choose different points in the square, including each of the four corners, and make note of the RGB values. What kind of colors do you get, and what RGB values make up those colors?
You should see that the lower left color with a high red value and low green and blue, yields (no surprise!) intense red. The upper left corner has a high red, high green, and low blue, and yields a yellow. The upper right has high values for all three, and yields a white. Finally, the lower right has high red, high blue, and low green values yielding a magenta.
You should see that the lower left color with a high red value and low green and blue, yields (no surprise!) intense red. The upper left corner has a high red, high green, and low blue, and yields a yellow. The upper right has high values for all three, and yields a white. Finally, the lower right has high red, high blue, and low green values yielding a magenta.
Now move the slider until R = 127. Note that the red corner is opposite a blue green called cyan. They are complements, and when you add red to an image, you are subtracting cyan, and vice versa. Also note that the green corner is opposite the purplish red called magenta. These are also complementary colors. When you add green you are subtracting magenta, and vice versa.
Now, select B for blue. Move the slider until B = 127. Note that the blue corner is opposite a bright yellow corner. They are complements, and, sure enough, when you add blue to an image, you are subtracting yellow, and vice versa.
