Jimmo: "My observation of real brick structures has shown me that mortar is rarely ever white." I agree. In fact, I think the only truly white mortar I've ever seen was painted. Most of it seems to be more of a "light cement gray".
That's why I specifically used their light gray for my two test pages. Especially in an industrial/mining town with nearby rail traffic the mortar certainly won't stay white. Also, the sand used in the area I model isn't white to start with, so the mortar wouldn't be pure white anyway. Besides the variety of brick patterns they also include quite a selection of mortar colors, and, if you're good with hexadecimal color codes, you can make up your own. I'm not, so I stuck with the preset custom colors, under "Browse Mortar Colours".