You're not the only one who examines betta poop on a daily basis!
I would just continue to monitor it. Hopefully, the strange color was just a one time thing. If it happens again (when you don't feed a pea), let us know.
He should be better with the Omega One. (I have a betta who gets constipated a lot. He's been much better since I started feeding him Omega One pellets.)
If he gets constipated again, ask your parents if they have any Epsom salt in the house. If they don't, you can pick it up at Walmart, a pharmacy (like CVS or Walgreens), or a supermarket. It should cost about $1.50. Make sure it contains just magnesium sulfate. (There should be no dyes, perfumes or additives.)
When he gets constipated, you can use about 0.25 teaspoons Epsom salt per gallon of water. Take a small amount of water from his tank, dissolve the Epsom salt in it, and pour it slowly into his tank.
Epsom salt has a laxative effect. It may take a day or two to work, though.
Then, when you do the next water change in his tank, just use regular water (with conditioner). Doing this will remove the Epsom salt.