This is a two piece Rollerball pen, gold color, where the cap is postable on the body when using the pen.  The body is made from a purple acrylic.

This pen uses a standard rollerball refill (like a Schmidt 888).  To replace the ink refill, remove the cap, point the pen body up, and unscrew the tip and remove the old ink refill (keep the pen pointing up as there is a small spring in the pen that you do not want to fall out), replace the ink refill, and screw the tip back on,