Hey!...Very nice!! Looks like you are well on your way. Good luck with the waterfall and keep us posted.

I like your rocks. I'm considering making 2-4" thick sandstone-like rocks for a similar edging. I plan on dry stacking them. How did you get the varied coloration in your rocks? How did you get in the nice lateral striations? Good job. - Mike

Mike-
For the color I use Quikrete brand liquid cement color, I bought it at Home Depot for about $6 / 10 oz. It uses iron oxide pigments and can be diluted in water, I only bought the Terra Cotta color and the Black. There are more colors.
I let my rock cure until solid but still green, depends on your hypertufa mix. Using aluminum pie tins I mixed the two colors in some and just used the original color alone in other tins, then diluted with water to about 1/4 cup. I ended up with a half dozen pie tins each with a different color and/or shade.
Apply with a paint brush in a dabbing manner. I use the chip brushes you can buy at Wal-Mart for less than a dollar, they come in several sizes. Sometimes I'll even use old art brushes - the more beat up the better! Don't use too much color on the brush and use several of your mixed colors on each rock. I keep a bucket of water to rinse the brushes as I'm working so I don't end up with one color.
Since the Tufa is still green it soaks the colors up; you can use a sealer after it has completly cured.

For the striations, cracks and some of the shaping I use several different sizes of plastic puddy knives. I found for striations it is best to work with the beveled edge up and just poke at the rock.
I'll tap over the striations with a rag or a gloved hand to remove that manufactured look