A programmatic approach using [`Trace`](http://reference.wolfram.com/language/ref/Trace.html):

    Trace[
      BulletGauge[{1, 1.8, 3, 3.4, 4, 5}, {2.4, 2.9}, {0, 3.5, 4.8}],
      _ColorData
    ] // Flatten // First

>     ColorData[63, 1]

Check:

    ColorData[63, "ColorList"]

[![enter image description here][1]][1]

Related examples:

- http://mathematica.stackexchange.com/q/71891/121

- http://mathematica.stackexchange.com/questions/112945/extracting-unknown-colorfunction-from-plot-plot3d-etc/123155#123155


  [1]: https://i.sstatic.net/BfSNU.png