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.
An alternate VT02 version of this game exists which removes the intro and changes the title screen. (While Aim Cruise uses the same background graphics for the title screen and gameplay, this version only changes the title screen graphics.) As a result of the graphical changes, the hidden credits screen is now garbled, and it looks pretty nasty.