This pen was shown to me by Mike Carter at the Washington DC Pen Show held in August, 2005. It has a rather unusual color which I think was attained by heat treating the base metal, which I believe to be sterling silver. This belief is founded upon the weight which I measured the cap at 7.4 grams while the barrel is 7.5 grams, the same as the Keepsake in its latest incarnation with the dished tassie and larger arrowhead clip. Both tassie and clip attributes are found on this pen as well.
For the above reasons, I call it a Keepsake Rainbow.
The surface of this pen feels as though it has a protective layer of some clear varnish.
Here is a close-up of the colors.
This prototype is for sale. Contact Mike Carter directly.