How to do this color replacement?

[sneaky]

I want to do color replacement in a special way, so is this possible to do in photoshop?

I am using cs6 beta at the moment.

Is it possible so that if I set a specific color of purple as foreground and white as the background, then is there a tool, that while i have the cursor held and dragged, it replaces all white pixels with that purple one, and ignores any other colored pixels. This should only happen is the color hex for the pixel matches with the color set in the background.

If I try the color replacement tool, it doesnt work...

 

[Hoogle]

colour replacement will not work with white or black pixels

how complicated is your shape.

 

[sneaky]

The image is below, I had a 3d model be unboxed into an image so I can do some texturing.
Basically I want to select a part of it using the magic wand tool or rectangle select tool, then
use this "replacement" tool to just hold/drag inside the selected region and replace the white pixels with
the forground color, and leave the black pixels (which are the lines) untouched. So this will allow me to paint
inside the black lines in the selected area.

 

[Hoogle]

create a new layer under your image by unlocking the background and fill it with the desired colour

then set your actual image layers blending mode to multiply and you get this