HELP:Toilet:Discolored Water "Backing In"...

We have a great toilet that has always flushed well, clockwise spin to
the water, and rarely needs a second flushing.

Lately, the water that refills the bowl is a murky, almost
yellowish-white color. Sorta' urine colored, but obviously not urine.

The water seems to be *backing in* to the toilet...the water in the
"closet" (the back of the toilet) is completely clean and clear. The
murky yellow-white, almost even foamy-ish stuff seems to be "backing
in" from that area where the emptying occurs (above that wax
ring...forgive me, I'm an amateur, and don't know how else to describe
it; that area of a foot or so above the ring).

I want to avoid a plumber here, cuz we're broke as heck. I'm going to
use a plunger tomarrow to attempt to dislodge anything that may be
causing the coloring within the first few feet of the flushed
material, but somehow I don't feel that will resolve it. It's as if
someone's put an alka-seltzer in the toilet that seeps it's
yellow-white liquid back into our bowl every time we flush it. Has
gone on for 2 days now, and does not seem to be coming from the
water-refilling at the top rim, but instead is "backing in" from the
bottom exit hole. I dunno. SEEMS to be. Hard to tell.

Does anyone have any idea what is causing this coloration? Has never
happened before, always been a clear clean water that refills the
bowl.

Thanks a bunch...I look forward to any/all opinions. I've come here
for toilet help before, and thankfully, have received a great deal of
help each time. (What is it about TOILETS?!?)...

Thanks again. HELP NEEDED!