Personally, I think something with small leaves would look most attractive in it. I think I would lean toward a variegated leaf. I have a succulent, with very, very, tiny leaves, that is tricolor green/white/pink and trails that I think would look super in it. You might think it would blend to much with the cup color, but I really don't thing so, the size of the leaves being so small, seems like it would be dramatic--oversized cup, miniature leaves. And if you wanted more heighth, isn't there a dracena that is pink edged? Or add a haworthia, "Little Zebra Plant" (Haworthia subfasciata). Consider pink ice plant, pink and white portulaca (maybe some yellow too), pink adenium (until it outgrows the cup), miniature variegated ivy.
