Blended color replacement

Question

I'm unsure of the terminology here, so I'll explain by example. I have an icon image like this:

i.e. an alpha-blended image with a single hue, as well as black and white. I want to be able to programmatically do a color replacement to a specific color, but retain the blending.

For example:

var blueCar = ColorReplace(redCar, Color.Blue);

To produce:

You get the idea! I want to do this with a specific target color rather than a HSL change as you'd do in something like Photoshop / Paint.NET.

I'll be using C# for this, preferably GDI+, but am open to using other free libraries if necessary.

Answer 1

I think you have to change the image pixel by pixel, as shown at CodeProject, though that is rather old. Sayse has created some sort of extension for bitmaps here that may be of use.