[updated 4 April 2011 - removed irrelevant first paragraph]
New companies and products need logos and it is important to get these created without too much fuss. To help with this it is useful to have some design rules. The 22 Immutable Laws Of Branding states that:
16. the law of shape :
A brand’s logotype should be designed to fit the eye and there is a natural ratio for a logo of 1 unit high by 2.25 units wide.
17. the law of color
A brand should use a color that is the opposite of its major competitor’s.
This guidence can form a useful part of your Product Description for the logo and marketing materials and help prevent a “Missy the cat” type situation with your designer.