I don't know why it was red before. I'm guessing they just changed the design. If it's really of importance to do, you should ask the italki team.

You became a premium member by at least uploading 10$ to your account. This means you can send out an un-limited number of friendship requests, post an un-limited number of discussions and notebook entries and you can take lessons. You keep the premium status for one year after your last payment. See details here: <a href="https://support.italki.com/hc/en-us/articles/206353358-What-is-Premium-Membership-" target="_blank">https://support.italki.com/hc/en-us/articles/206353358-What-is-Premium-Membership-</a>;

Why was it red before and how did I obtain this status ?

The purple ribbon that you have, means that you're a premium user.