RODENT TEETH, and why are they yellow?

[Die Fledermaus]

Here is a to a very interesting article on rat teeth; all rodent teeth are naturally yellow:

www.ratbehavior.org/Teeth.htm

>> Question - I have had many people ask me, while I was showing off a
beaver skull, why they have yellow-orange incisors? I know beavers are
rodents, and their incisors are constantly growing, and I have noticed
this in all rodents also. But why is there a discoloration of the incisors
(only) and not the other molars? Thanks!
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The incisors are composed of two different materials, the outer, colored
portion is harder, the whiter inner portion is softer. When the animals chew
the softer material wears away faster than the colored, harder part so that
the teeth are constantly sharpened as they wear and grow. I assume that the
difference in color is simply due to the different composition <<

www.newton.dep.anl.gov/askasci/zoo00/zoo00421.htm

From Wikipedia:
>> The mineral distribution in rodent enamel is different from that of monkeys, dogs, pigs, and humans. In horse teeth, the enamel and dentin layers are intertwined, which increases the strength and decreases the wear rate of the teeth. <<