Funny BB, About a year ago I tried to make my own using grey and black as I wanted to match the rock color I was going to use for my waterfall. The few I tried turned out Ok. Yours actually looks fine. Did you do that as a sand cast mold or?
I dug out a hole to a shape and put a black plastic bag in the hole and then poured the cement mix. I only tried it once as I got busy on the pool project. I still plan on a mini type pond by my shop.
Maybe someone can start a DIY project thread and we can all post in one thread.