The situation when someone is accidentally or intentionally exposing (showing) colors from their clothing that relate to a gang 'color' causing alarm or suspicion from anyone that notices, especially authorities such as the police.
Young individual walking in the mall wearing all blue: hey why the hell are you questioning and searching me as if I'm carrying any weapons?! What is this the gestapo, I thought this was a free country, I could wear whatever the hell I want!
Two undercover cops: well there's been a gang stabbing here earlier and you were 'flashing colors' (wearing all blue).
Reffering to a police lights which flash because of a person breaking the law while they observe it via police cruiser
or
the result of papparazi taking many pictures
or
a song by rapper Kanye West off of his recent album "Graduation"
"man, you gotta stop! there cops ar FLASHING LIGHTS!!!"
"those FLASHING LIGHTS are going straight to Tmz"
example of lyrics from flashing lights by kanye west
"I tried to hit you with the o wokie
Till I got flashed by the paparazzi Dang these niggers got me
I hate these niggers more than nazis"