Pen with selective multi-color cores

A marking pen with a plurality of colored cores comprising:

• a pen body comprising a hollow tube having a top end, a bottom end, an inner wall, and an outer wall, and a plurality of elongated tube-holding projections on the inner wall of the pen body;
• a recessed groove at the top end of said pen body;
• the bottom end of said pen body being cone-shaped and comprising a plurality of core outlets on the exterior thereof;
• a pluriality of core-receiving tubes housed in said pen body, in the tube-holding projections, each tube having an oval cross-section and a smooth three-faceted top end, a small groove on the topmost end thereof, and a hollow interior containing fluid-absorbent material for storing ink, and a core at the bottom end;
• a spring removably disposed on the bottom end of each of said core-receiving tubes;
• a turnable knob comprising a top cylindrical portion and a bottom cylindrical portion, the top portion and bottom portion having differing diameters, the top portion thereof being denticulated externally, and a groove disposed on the bottom portion thereof;
• an opened ring located partially on the bottom portion of said knob and partially in a recessed groove on the inner wall of said pen body;
• a projecting edge on the circumference of the bottom end of said knob which is in cam engagement with the three-faceted cam surface on the top of a core-receiving tube to enable the tube to be pushed downwardly to allow the core to project out of said core outlets;
• a cap attached to the bottom end of said pen body.