The standard way to highlight selections in MS GUIs is to invert the colors. So what you do is get access to the image bitmap data (
Work with bitmaps faster in C#[
^]) and 1-complement the desired pixels.
Alternatively, you can think of increasing the luminance by multiplying all three color components by a common factor (say
1.33
), but you will need to limit the factor to avoid saturation, that could induce a color drift. So in practice, use
Min(1.33, 255. / Red, 255. / Green, 255. / Blue)
. For this reason, luminance enhancement will not work on already light areas.