Painting the town red
When members of Team Valor go from gym to gym in Pokémon Go, battling them and claiming them for Team Valor, it is said that they are painting the town red.

For Team Mystic is is called painting to town blue.

Towns do not get painted yellow very often due to the lack of number of players on Team Instinct.
Her and I went out last night to play Pokémon Go, we were painting the town red.