The paint won't hold up when it's mixed in, kind of pale muted colors. They wash out completely in a short time in the outdoors. If you add too much paint to the mix; the mixture won't cure. Billie

Thanks for your reply. I guess I'll forget that idea and just paint the surface or use dye if I want color.

I always come back to painting my "stuff". I've had craft store acrylic paint hold up for quite a few seasons. It holds up even better if you seal. I don't both sealing. I re-paint if I want to, most times I don't. I also use wood stain. I usually don't paint the whole thing, just accent. Billie

laura,
I love using color--I made a couple moons that hang in front of my house--molded in metal barrel rings about 3 inch thick. The one quarter moon was colored by the "stab" technique (my term). I just sprinkled red and black oxide in a random pattern on my wet qtr moon and stabbed it in with a chop stick which also gave it a knarly texture in the areas where I stabbed it in. The full moon has black oxide across it and looks like clouds on a white moon. Basically, as long as it a mineral based dye/colorant it can be used but to excess will compromise your mix strength. I would stay away from paint as an integral--surface colorant is fine for paint. That's my story and I'm sticking to it. Hope this helps a little.
TB

Both Homer and Lowes carry cement dye that is used for casting stepping stones and the like. Is there any reason that it wouldn't work in the tufa?

the liquid dyes found in the concrete department work great but the color selection is limited to 4 colors.

More colors - powder - can be found at some concrete suppliers. And then as Billie suggested you can always use craft paints.

Mike

Thanks to all of you for the suggestions. Where can I find oxide?

Look in the yellow pages for a place that sells concrete supplies in your area. Most likely they will have powered colorants for cement. It maybe be cheaper that this link that I am providing.

Here is a link that might be useful: examples