Oh, wait. Wrong series. Sorry. :D
The rules of heraldry have evolved over time to be quite strict: while you can break them, and pull out any old colour from a paint pot and slap it on a shield (and believe me, I've been guilty of that before now), it helps to know what they are before you start.
To begin with, heraldry draws from a restricted palette of what are properly called tinctures, not colours. Tinctures are divided into three groups, and within each group the tinctures have names, largely Norman French, but sometimes not.
The first, and most numerous group, is the colours. (Yes, 'colour' has a specific meaning in heraldry, so be careful.)
There are more than four colours, before any heraldry buff goes 'but what about..?' However, these are by far and away (and hopefully obviously) the most common, and I'll cover the rest in a later article - note that some sites list a slightly larger different set of most common colours, but I'm going by what my edition of Boutell says.
Right about now, the non-heraldry buffs are probably also going 'but what about....?' for a different reason, so lets move on to the second group of colours, the metals.
In addition to colours and metals, there are a third category, furs. Furs are semi-stylised representations of various animal furs. For now I'll restrict myself to the most common two, and save the complications and variations for another post.
There's also one extra... well, I'm not sure whether it's better described as a collection of tinctures or in some senses just one, and that is proper. Proper means 'in its natural colours'. With a caveat that heraldry's idea of 'natural' can be a little odd sometimes.
So, there you have it: enough tinctures to make some quite interesting shields. Next, the shield itself.