Heraldic rules for clan coat of arms

Just an idea I had, not too sure what I feel about it myself:

in addition to the rules for custom clan emblems you could make every picture adhere to basic heraldic rules: 

metal should not be put on metal, nor colour on colour

Metal heraldically speaking would be golden and silver, represented by yellow and white.

Colors are blue, green, red, black and purple.

So you could have a white lion on a red background or a red eagle and a white background, but not a white lion on yellow or a red eagle on blue.

There also wouldn't be different shades of the same color present, except for stylistic reasons: a lion can still have different shades of yellow to hint at shading on the fur for instance.

The advantage would be that it's both clearer to recognize and historically accurate.

The disadvantage might be that it limit's creativity.