I would spray paint that yellow filter top black or cut some black plastic to fit. Everything looks great but that yellow really sticks out - should be an easy fix tho.
I'm personally not crazy about the white pots and rocks on the platform - they stand out too much to me and make it look too busy. It's not bad - don't get me wrong - just not my personal style. I would probably use matte finish black pots and black or dark grey rocks, and I would use alot of rocks and "nestle" the pots down into them. I'd also pile them up a bit around the filter box (unless you need to move the actual box often?) so it would look more natural. And while I was at it I'd paint the fence a deeper color - I'd probably do something like a very deep, dark rusty red. And then I'd add the same color cushions to the chairs on the patio! LOL! I sure wish I could do a project like this I would LOVE it. But it's cold here in the winter and I wouldn't have space to move everything inside.