One way to colour your soap is to use natural colours.
There is a large range of plant powders you can use to colour your soap, most of them will give your soap muted, earthy tints. I find they work great in natural soap as they emphasize the natural provenance of all ingredients used in your soap.
What natural colours can you use?
Plant powders:
Turmeric for yellow to orange (depends how much you use. For a light yellow let the turmeric seep in olive oil and use the liquid only. Or for an intense colour add the turmeric powder directly to the soap);
Paprika powder for orange (please make sure it’s not smoked paprika or even worse hot paprika!);
Cacao for brown (the pure powder with no additives, not cocoa which contains sugar and other additives);
Activated charcoal for black;
Indigo plant powder for blue;
Naturally coloured clays (pink, light orange, green, brown);
Alkanet for blue, but sometimes it turns grey;
Madder root for peach colour;
Orange peel for orange;
Green tea powder for yellow-green;
Moringa leaf or spirulina for green.
Please see below a video of mixing your soap batter with activated charcoal.