There are a limited number of tinctures allowed in heraldic arms, probably because there were limited choices available in the middle ages. Traditionally, we have:
the Colours the Metals and the Furs.
Over time a few more have been added, but these are the basic tinctures. If you go back to the blazon you will see the descriptions of shields and devices using these colours. The first tincture given is the "field" or background, followed by those of the objects or devices on the shield. For example "Sable, a lion rampant Or" might look something like this:
The "sable" is the background and the rampant lion is gold. A general rule of heraldry is that a metal object may not be laid on a metal field and a coloured object may not be laid on a coloured field is that a colour must not go on a colour, nor metal on metal or fur on fur.
If something, such as an animal, is shown in it's natural colours, it would be described as "proper" (i.e. an arm holding a sword, all proper).
As noted earlier, this is a very brief look at heraldry. To learn more, you should get hold of a good book on the subject.