Get to the vet.
Now.
It might be anemia from some minor condition (fleas, ticks), or anemia
from a major condition (cancer, organ failure)...or it might be blood
loss from internal trauma.
A long time ago, my quick response to this condition saved my dog's
life. Her spleen had been twisted around (we think she tried to jump the
fence and missed) and the blood was gathering in it, but not leaving.
Quick surgery saved her life. Had I waited only a few more hours, she
would have died.
My cat was anemic when she had a URI. No huge biggie.

Either way, pale gums means low iron or anemia. It's the cause you need
to worry about. If it's something minor, you worried about a little
thing. If it's something major, you saved her life. Better safe than
sorry.

Only the vet can tell you what the problem may be.  However, do you have
good baseline knowledge of exactly how pink your cat's gums and nose have
normally been?  Cats are normally paler in coloration than dogs, and when
examining a cat, "cat pink" i.e. a healthy pink coloration, is several
shades whiter than a dog or human. Please do take your animal to the vet for
examination though, and let them be the judge, not an internet newsgroup
that can't see your cat in person. If it's normal coloration, they'll tell
you.  A sudden paling or any other abnormal condition should always be
investigated by your vet *first*.

Yes, my guess is anemia.  Your cat needs a vet appt., ASAP.  If the vet also
suspects anemia, a quick, in-house blood count - PCV (packed cell volume) -
can be run.   If your cat's anemic, then the vet will probably run more
tests to find out *why* s/he's anemic, to get to the root of the problem,
besides just treating a low blood count.

Cathy

--
"Staccato signals of constant information..."
("The Boy in the Bubble")  Paul Simon