Gan Gogh originally came across the Rainbow lights twenty-four years ago and he tried to draw them using seven different crayons, he was unable to get it right though. So twelve years later he tried using twelve crayons instead, which also was a futile attempt. However, this time he made sure to come prepared with a full arsenal of two hundred fifty-one crayons. Ash comments on how he saw the Rainbow Lights earlier before arriving at the Pokémon Center, which results in Gan Gogh asking Ash where he saw the lights from. When Nurse Joy subsequently maps out where the lights must come from, it is determined that their origin is as the place formerly known as Remoraid Lake. Brock then brings up a legend he heard about the Remoraid at the lake being very difficult to catch, resulting in Misty asking how can Water-type Pokémon be living in an empty lake anyway. After this question is posed, Team Rocket arrives posing as archaeologists, with Meowth disguised as a Mummy. After this unexpected arrival, the lights suddenly appear in the sky again, however are gone before Gan Gogh has time to choose a crayon to start with.
(Source: Bulbapedia)
