Use enamel-based flat-finish spray paint in the brick color of your choice and apply a thin coat to all surfaces. Let dry for an hour and apply a second coat that completely covers. Let dry overnight.
Sand down any "burrs" that may have arisen on the smoother surfaces of the chimney collar and ledges but leave some roughness. If "burrs" have protruded into the routed mortar lines, use an emery board to sand them open. Do not sand so vigorously that you expose an unpainted surface. If you do then you will need to re-apply spray paint evenly and let dry overnight.
Lay the fireplace down on its back. Use a small spatula to stir and apply a thin coat of #2076
Mortar Mix over the surfaces including the chimney collar and the ledges. With a damp sponge, wipe away excess mortar from the surface of the bricks. Rinse the sponge, squeeze out excess water and repeat wiping until most of the mortar residue has been wiped off of the brick surfaces. Dab the sponge on the flat surfaces -- the collar and ledges -- to create an even but slightly rough surface. Complete mortar coverage on these areas is not necessary.
Turn the fireplace on one side and repeat the above process then lay it on its face and finally on its other side, working your way around.
Stand the fireplace upright and make final dabs at the mortar coverage on the collar, ledges and chimney top. Let the mortar dry for a half-hour and wipe only the brick surfaces with a slightly damp sponge. Repeat drying periods and damp wiping until brick surfaces are mainly free of mortar residue. Then, let the mortar dry overnight.
For a uniform concrete or limestone look on the chimney collar and ledges, use craft paint in black and a shade of light gray applied with a small stippling brush. Cover adjoining brick surfaces with masking tape to shield them. Pour out small puddles of the two paints on a sheet of wax paper. Dip the brush into one color and dab it randomly on the surface to be colored. Dip it into the second color and dab over the same area. Continue dabbing the alternating colors until the surface is coated with multiple hues of gray. Remove the masking tape and use a slightly damp paper towel to wipe away any paint that may have seeped onto the brick surfaces. Let the paint dry.
The inside of the fireplace and chimney are painted solid black.