How to change a specific color

I am not sure whether this is what you are looking for but if it is, you will find you can separate the type from its backgound by using the Blend If Command. Then, with this image placed in register as a layer over the original image you can make the type any value you choose. Be aware, though, this is a photo image. rather than type and the edges may not be adequate for your intended use. 

You have pixels only? Do you know that selection can be substracted too? I mean after selecting something you can grab Lasso, Polygonal Lasso or Rectangular Marguee tool to deselect area from current selection. After activating tool look in the Options bar for 4 icons and click on third one: Subtract from selection.