Fantastic question. Herein lies the answer.
My Colleges is a feature that allows you to add any college of interest. You are then a part of the "Interested" Community of that college. You can see others that are interested and match based on your passions and interests. In some groups, you can also view counselors at a particular college and learn more about their school and them personally.
Once you are accepted to a given college, you can upload your acceptance letter and enter into the super, secret, "Accepted" group. Inside the "Accepted" Community, you can see who else was accepted, who is going and match with a roommate on the best roommate finder of all-time. No bias here.
Do Colleges See The Other Colleges I have added?
No. Colleges that you add can see if you are in their community on the mobile app, which is a good thing, because they know you are interested. :) However, we don't reveal to any college the other colleges you have added.