Limestone is actually one of the most common stones used in bridge building, and is famous for its use in large municipal buildings. One reason is because it cuts easily.
Pure limestone is almost white. However, that is rare. It depends on the region and upon the weathering it has taken. Limestone weathers easily, and is very susceptible to water erosion...hence the sinkholes and caverns in the east. In regions with heavy iron content, it takes a reddish-brown hue. In the Virginia/WVa Alleghenies, it is commonly grey, with white splashes, or brownish in weathered spots or in areas where sandstone has washed upon it.
Here's a photo from a Virginia limestone quarry:
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