Brief Answer:
Most probably it is not feces

Detailed Answer:
Hello,

Thank you for using Healthcaremagic to post your health query.
I read carefully your question and I understand your concern.

I think that the fece-like vomiting parts, may most probably be just food changed by the enzymes and the acid of the stomach.
If it was feces, you would also see bile (very green liquid) in the vomit and also the vomiting will be very strong (the feces are localized after the sphincter of the stomach which is very hard to allow the liquids move backwards.

On the other side, the colon cleanse meds, work by stimulating the bowel to contract faster, so it is not possible for it to work backwards.

So basically I am telling you that most probably it is nothing.
If you have these types of vomiting again, I would recommend to take a picture of if and post here so I can have a look.
Also, let me know if you feel worse, or not better, or if you start having any other symptoms.
It really does not indicate of being something relevant with the information I have. But the more information you give to me, the more I will advice accurately and help more - Any other symptoms? Why are you taking the colon cleanse pills? Do you have any chronic problems that you know you suffer from? Any other medicines? ect

Hope this is helpful.
Let me know if you need more clarifications.

Regards,
Dr. Papaqako

---