A monochromatic colour scheme is using different pigments of one colour throughout a space, it is a great way to create a calming space, with a muted delicate look. When done correctly you can still achieve a contrasting look with vibrant focal points while using one colour.
When doing a monochromatic room, you can add a bit more excitement by adding multiple patterns and textures. This allows you to create a wow factor or focal point without adding in additional colours.