Colour can evoke emotion, capture attention, and send a message. Whether you're designing a logo, business cards, a website or a retail environment, choosing the right colours is critical. Here, I'll review a little colour theory as well as how to choose colours using a gadget that dates back to the 17th century.

Colour theory 101

A colour scheme (or colour palette) refers to the group of colours you use in a project, a painting, or your living room. You as a designer usually picks a main colour and then chooses the other colours according to how they look together and the feeling they evoke when they're viewed as a group. There's a whole science behind picking colours based on what they mean to us humans and how they make us feel, as shown in the image below.

Those meanings and feelings can differ according to geographic location. For example, hospital rooms and public spaces are typically bathed in pale blue or green because those colours have a soothing effect, while Apple stores are predominantly white to reflect a feeling of elegance and simplicity.

 
Here are a few examples of how colour communicates to people in the UK, United States and many other Western countries.

To learn more about how colours make us feel, pick up a copy of Pantone's Guide to Communicating with Colour by Leatrice Eiseman or purchase the Galaxy Colour Map Pro ($15 plus shipping), a fold-out, laminated guide to finding and specifying CMYK colours (great for print designers). It also includes a colour wheel as well as a colour emotion chart.

When dealing with colour, especially in software such as  Photoshop, you're likely to encounter the following terms:

Hue is a term for pure colour, before it's had any white or black mixed with it. Pure colour mixed with white is called a tint because it produces a lighter colour than you had before (blue plus white equals light blue). Pure colour mixed with black is called a shade and produces a darker colour (blue plus black equals dark blue).

Saturation describes a colour's vibrancy. For example, a highly saturated hue has a vivid, intense colour. A less saturated hue looks dull and gray. When picking colours that will appear side-by-side, it's helpful to use similar saturation values.

Brightness determines how light or dark a colour appears. You can think of brightness as the amount of light shining on an object, ranging from white (100 percent) to black (0 percent).

Using a colour wheel

The simplest way to pick colours is to use a colour wheel – a circular diagram of colours arranged by their relationships with one another. A colour wheel is based on the three primary colours: yellow, blue, and red, from which all other colours spring. By mixing equal amounts of the primary colours, you get a second set of colours called secondary colours. Mixing equal parts of the secondary colours gives you a third set of colours called tertiary colours. Together, these colours comprise the colour wheels shown below.

 
A typical colour wheel is made from primary, secondary, and tertiary colors. While Sir Isaac Newton first arranged colorus around a circular diagram in the late 1600s, one of the earliest known coluor wheels, dated 1708, is by the French painter Claude Boutet (it’s based on Newton’s diagram).

Using a colour wheel is a two-step process: start by picking the main colour you want the colour scheme to revolve around – the colours in, say, a logo, a photo, or a canary-yellow couch--and then find the closest match to that colour on the colour wheel. Next, use one of the following colour-scheme rules to identify where on the colour wheel you should look to find other colours that go well with the first one.

Monochromatic schemes use colours from the same wedge of colours on the colour wheel. Analogous schemes use colours from the wedges on both sides of the main colour. Complementary schemes use colours from the wedge directly across from the main colour.

 
There are numerous colour-scheme rules, though these three are among the most practical and easiest to memorize. The main colour in this scheme is blue, which came from the photo (marked by the red rectangle).

Most colour wheels have a spinning-dial component that you use to point at your main colour, and then a series of arrows that point you to associated colour wedges for a particular colour-scheme rule, as shown here.

A colour wheel won’t turn you into the next Matisse, but for most mortals it’s the tool of choice for pairing colours. The one on the right has little windows that you can use to see how the colours you’re considering will look next to the real thing (say, a piece of fabric or spool of thread).

Using a colour wheel is easy, once you get the hang of it. And when you do, you'll be picking perfectly pleasing palettes in no time.