Utmost Warfare is not one of the many entries in the Call of Duty franchise, but rather an absolutely horrendous shooter which features confusing graphics and a final boss which is completely nonfunctional.
As with many Nice Code games, pressing Up, Down, Up, Left, Right, Left, B on the title screen will briefly display a credits screen. Nature Color Game is one of several aliases used by Nice Code, and PJ most likely refers to the Power Joy series of Famiclones which many Nice Code games have been released on.
The game features graphics for an ending screen, inaccessible through normal means as the game's boss is broken and cannot be defeated as a result.
An alternate version of this game exists which replaces the title screen and music. The code to access the credits screen was disabled and the gate that appears at the end of each level is now corrupted.