Mix type N mortar mix and type M mortar mix

I have worked with dry color for concrete. We poured a few slabs and some curb.

The dry power was available at a concrete supply house. It was expensive, but could be bought in small bags if needed. A little went a long way.

The color powder made a huge mess and stained everything. It was the consistency of powdered sugar. You need to mix it really well with the dry mortar or you will end up with varying color. You need to test the color by mixing up and curing a sample as it is hard to know exactly what the color will look like until it cures.

In this case, I would skip the color and use polymetric sand. Something like this: http://alliancegator.com/2011/?p=21

you could use a Construction adhesive like Liquid Nails or Beats the Nail. This works well for cap stones, since they are usually not a structural part of the wall.