Why is white light more visible than red and green on this Cessna model on a sunny day?
The navigation lights are meant to give away the airplane's orientation (i.e. which direction it is travelling) at night. The red and green lights are small. Their purpose is to be observable from a long distance, which only requires a small light. For the same reason, the anti-collision red lights of tall structures are small as well.

The landing lights (white light) are meant to illuminate the runway, taxiway or any terrain in front of the aircraft. The light must travel to a certain distance in front of the aircraft then bounce back. They are very bright. To experience that, go to a busy airport at night and stand near the approach end of a runway. In fact, standing next to an airliner with its landing lights fully on would likely damage your eyes.

Landing lights must also be turned on when any aircraft enters an active runway. Here they serve the same purpose of turning on the headlights of your car at night: to make sure others can see you. This regulation came after an airliner landed on an occupied runway at night. It was determined that the plane on the ground blended in with the runway lights, and the pilots of the landing aircraft were unable to spot it. Had the plane turned on its landing lights, the very bright light source would have give away their position and alerted the crew to abort its landing.

The model is simply a replica of the real life scenario.