Again, in Dawnbringer32. Uses a total of 24 different tiles (not counting palette shifting). Here's a sample image:
Oooh, very nice. I personally don't think dithering should be used on metalic objects unless you're making it rusted and pitted, but that's because of the texture. I like it very much.
I tried without dithering at first, but it didn't feel like there were enough colors for it to look good that way. I'll poke around at it and see if maybe I can make it work.
Just for kicks, I added a set of pipe tiles without dithering.
They look a lot more metalic now, though I think you may be right that they might need more colors. That shouldn't be too hard to do though, since metal picks up surrounding colors really well you can get away with putting in just about any hue as long as the luminosity is right. I actually like the dithering kept on that one in the background, it helps it be a background piece and gives the impression of being in shadow.
Be careful with the highlights on the pipes. As it is now the visual priorities are a bit confusing. Usually you want the brightest thing there be the thing the player can stand on.