Yellow stool means a faster than normal transit. It is the bile. It starts out bright green and changes to yellow, then brown, as digestion progresses. It does not neccessarily mean illness, but could be is you were exposed to a virus or bacteria that causes a gut infection. If that is the case, it would blow over in a few days, or get so bad you seek medical attention. But, if it is just your normal fast transit, yellow could be typical. Slowing peristalsis with Imodium or lomotil should help. Fiber, like Metamucil, does not slow peristalsis, so it would not affect color in a significant way.
The main thing is how you feel. If you feel well, don't worry too much about it. If your stools turned a pale clay color, then it is something to pay attention to. That would mean your gallbladder was obstructed.
Jan