I've never heard of them, either. Sometimes a young GT can be faded or very light and some have more blue/turquoise and less black on their scales than others-- with some of the nonsense names I've seen people sell fish as sometimes, maybe someone somewhere has attempted to sell one of these as a 'platinum'. I've seen GT/electric blue acara crosses, they don't seem consistent and it typically makes an odd looking fish (to me), not what I'd call a platinum, but again, who knows what someone might try to sell them as.