One of the great things about black and white pictures is you can make them any colour you want.
Why would you do that? Well, sometimes it can add to an image. Imagine a picture of an old sportscar, toned in British Racing Green. How about being able to control the subtlety of a sepia tint? How about adding a hint of colour that matches the paint on the walls (or is complementary)? Or toning the highlights in a scene slightly warm and the shadows with a hint of blue?
The last one – toning the highlights differently to the shadows – is split-toning and used to be really difficult using chemicals.
Rather than smelly stuff and plastic trays, you will need somethng like Photoshop: Elements is fine, as is any similar program that will work with layers and blending modes.
Open your base image and change the mode to RGB colour (in case it is set as Greyscale). Then do all the things you would normally do to make it look nice. To change just the shadows, add a new layer above the image that has blending mode Lighten. To tone just the highlights, make the blending mode Darken. Then fill the layer with the colour of your choice and play with the Opacity to tweak the level of toning.
The following set of layers –
Produced this picture.
If you wanted to tone with only a single colour, say for sepia toning, use a single solid colour fill layer above the image with blending mode Colour. If you want sepia, try filling the layer with the settings Red 210, Green 165 and Blue 90. Again, play with the opacity to tune the effect.
So where do you get nice colours from? Or in other words, where do you find the RGB settings for the colour of your choice?