The price differential settles at about the cost of coloring plus the perceived cost of the bother involved. The most desirable coloring is original color. Next would be recent color done in an authentic style. Least desirable is bad coloring, whether recent or original. Some maps were never issued colored, and knowledgeable collectors avoid colored examples.
Some sophisticated collectors believe that coloring obscures the beauty of any engraved map.
In the final analysis, it is a matter of taste. The blank margins on maps may have been trimmed at some time in the past. This reduces the value. Some maps, however, were issued with narrow margins. Because of this, there can be no general advice for the beginner, except to view narrow margins with a jaundiced eye.