Haha, I see both of them, too. Totally not intentional, I just took a sponge and a paper plate with some different shades of paint on it and went to town. Did the whole back in maybe half an hour, just dabbing different mixes of shades around. I like how hidden stuff can pop out of random patterns like that. I had a leopard print shower curtain when I was a kid that I could see so many odd faces and shapes in, and I loved it. I'm sure I'll be finding loads of things in the randomness of the background.
Thanks for all of the compliments! I'm personally very happy with how it came out, and I'm really happy to hear that everyone following along thinks it looks good. I just can't wait to show it off when it is complete with sand, water, rocks, and fish! I picked up 6 juvenile angelfish already, they are in the 20 gallon for now, just waiting for the big tank to be filled.