There are a few ways. The one that is most expedient (but not much fun)
is to create a new layer (or not) and then take Image - Adjustments -
Hue/Saturation and click in the Colorize box.
Another way is to change the new layer to Color Mode (in the Layers
palette) and then paint over in the colors you wish.
jj
Depends what you mean by adding a tint of colour.
If you mean adding an overall tint of one single colour to the entire image,
then you can do it using Image>Adjustment>Photo Filter...
If you want to add specific colours to specific areas of the image, just
create a new layer, set the blend mode to either Colour, Overlay, or Soft
Light, and paint your new colour into that layer.
Once done, adjust the opacity until you get a pleasing and natural result.
Assuming Photoshop.....
Make sure you're working in 8-bit mode with your B&W image.
Then: Image/Mode/Duotone.
You get the choice of Mono, Duo, Tri or Quadtone in the pop-up window and
you can play with the hue and levels for each.