[Gateway103]

One possibility, although not an effective way, is Image -> Adjustment -> Replace Colour

Set Fuzziness to 0, select the pixel from the image with the pointer, then adjust the Hue, Saturation, and Lightness to get the colour needed.

The selection process is simple and quick, but getting the right Hue, Saturation, and Lightness value can be quiet annoying (you basically have to eyedrop the desire colour, check its value, write them down...), if you need to preform this operation numerous times...

There are probably more efficient ways, but I can't think of any atm.

-Gateway103