Color pallatte question

If I am tracing over multiple areas of a jpeg file with very simalar colors, the eye dropper tool often produces one identical color. This brings me with the following question: Does the eye dropper tool have a database of its own, with a reduced number of colors separated from the viewable color pallette? And if yes, how many increments, both the X axis and the Y axis, does the color pallette contain on any given one on the color slider? If this is the case, are the specified in a linear, exponential or any other form (in size/dimensions)?

Any insight would be much appreciated.

Sand Patch