Do lights on wingtips change color at different times of the day?
Every plane has green and white lights on the right (starboard) wing, as in this photo, and red and white on the left (port) wing. These lights are called "navigation lights," and are the same as are used in boating. 

The green and red lights are always on, no matter what, and are used to help other aircraft know which direction the aircraft is going, based on whether the other pilot sees red, green or both lights. 

The white lights are also on all the time, and flash constantly. These lights are called "anti-collision lights."



(Image Source: Wikipedia)

What you are actually seeing is the green light constantly on, and the white flashing - but because the white is so much brighter and is flashing, it's more apparent than the green (which, especially in the day, is fairly dim)

At night, the green becomes more obvious and the flashing white becomes more visible. The flashing white over-powers the green, which gives an optical illusion that the Green is flashing. The reality is that the Green is always on, and the white is flashing.