You can invert a color by subtracting each of its red, green, and blue components from 255. In other words:
new_red = 255 - old_red
new_green = 255 - old_green
new_blue = 255 - old_blue
You can break a color into its components, use this technique to invert the components, and then use RGB to recombine them into the inverted color. However, there is a much simpler method.
If a color's components are given as R, G, and B, then the color is represented as:
R + 256 * G + 256 * 256 * B
Now consider the representation of inverse of this color with components 255 - R, 255 - G, and 255 - B:
(255 - R) + 256 * (255 - G) + 256 * 256 * (255 - B)
= (255 + 256 * 255 + 256 * 256 * 255) -
(R + 256 * G + 256 * 256 * B)
= &HFFFFFF - the_original_color
So a simpler method for calculating the inverse of a color is:
new_color = &HFFFFFF - old_color
For more information on advanced graphics in Visual Basic, see my book Visual Basic Graphics Programming.