Almost there! I've painted each column with a latex semi-gloss black for a base coat as seen here:
Then, I took some gray latex paint and brushed over the top of the black. Make sure not to cover up the black base color entirely. The black will be visible in the low parts (made by the water and blow torch).
Once this dries, I'm going to add a bit of white to my gray to get a little lighter color and use a sponge to hit it gently to make some highlights. Of course, you could add as many colors and shades as you like (green for moss/lichens, etc). If I have time, I may try some of those, but for now, this will be good enough.
Until next time...