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.