Three lucids is a great start, congrats!

I wouldn't recommend your RC though, because although it worked this time, your dream may not always make it purple/not purple. It's pretty much chance, which isn't as reliable as the nose-plug or finger-count RC. You were aware enough, from doing lucid activities in real life, that you realized something wasn't right when you looked at your finger, and proceeded to double-check. That's often how lucidity comes about; you suddenly realize something is off, or just that you're dreaming, and do a RC to make sure.

Your dream control seems to be pretty good, too.

I'm unsure if the subliminal lucid video is the cause, because it doesn't necessarily increase your overall consciousness in waking life or in a dream. If you read about lucidity alot, though, it might end up in your dream.