This involves using a single hue (i.e. one colour green, red, yellow, etc), and varying its tint and shade. As a result, the energy is more subtle and peaceful due to a lack of color contrast. This may sound like a dull idea to you, but the range of possibilities available from only one hue is in fact very large. Additionally, by using paints with different levels of sheen on different textured surfaces, different reactions to light will be seen, enriching the atmosphere.

An example of this would be to paint the walls a very pale peachy orange in a matt finish, having soft furnishings in a mid-orange, and accessories in a deep orange. See 'White for the Woodwork?' for suggestions on how to deal with the skirting, window frames and doors.
Neutral colours almost always work well and are definitely most popular when it comes to mono-chromatic colour combinations, but can sometimes be perceived as dull. More powerful hues can create a magnificent look, so don't be afraid to at least sample them.
Also, those colours that we consider to be neutral are not in fact completely neutral, as they always hace hints of non-neutral pigments which can make them look pinky, greeny, buttery, etc. On a large scale, these pigments will be easily noticed and may not give the effect that you thought you saw on the colour chart or paint sample.
Paint Library have a range of colours known as their architectural range which is ideal for mono-chromatic colouring. They have introduced the idea of taking a hue and then creating colours by changing the shade; from light to dark the same hue is numbered respectively from I to V. For example, the colour Chalk has five variations numbered Chalk I to Chalk V, the idea being that you use two or three shades within.