I started by looking through the image. After wondering for a bit, I began by adjusting the curves on a separate layer, where I found that a slight parabolic shape could touch-up the image well. Then I experimented with the Mixer, adjusting RGB to ratios of 8,8, and 116. Little changed, but from there, adding a Pop layer made the bricks over-colored. This light adjustment brings out the original color of the brick, and the mortar as if it had never faded.