Hi bitla.
I agree with Ken on this. Since these are not color pictures to start with, there is really nothing to be lost by desaturating the pictures to black and white. All you really have to do is add a saturation layer, and click the colorize box. Then adjust the color tone to what you want. It isn't necessary to desaturate first, as
ps will do this automatically when you add the hue/saturation layer and click the colorize box, and by skipping that step, you haven't destroyed your original layer, in case you don't like the result.
Dave.