From the Super Mario Wiki
A Flipswitch Panel, also known as a Switch Panel, is a type of switch that appears in Super Mario Galaxy and Super Mario Galaxy 2. They start off as blue panels with a question mark on them. The panel turns yellow with an exclamation mark when it is stepped on, but back to a blue question mark if it is stepped on again (the only exception is the Flipswitch Panels in the Gateway Galaxy, which all have circles on them rather than a "?" or "!"). However, a Flipswitch Panel will not change if Mario or Luigi jumps and lands on it again before walking off it; Mario or Luigi must step onto another Flipswitch Panel or a regular platform in order to change the color of the Flipswitch Panel. When all of the Flipswitch Panels are stepped on in a specific area, they turn green and display a square on them. After this has happened, they will no longer change. After this, an event will occur within the immediate area. A galaxy called the Flipswitch Galaxy has a planet made completely out of Flipswitch Panels. Sometimes Mario or Luigi will be chased by Cosmic Clones on Flipswitch Panel planets.
When Flipswitch Panels are stepped on, a tone is heard. The only exception is the panels in the Rolling Masterpiece Galaxy in Super Mario Galaxy 2, where no distinct tone can be heard and instead produces a strange atonal sound when rolled on. The tones always remain in harmony with the background music and its chord structure, though they are detached.
Flipswitch Panels appear in Super Mario 3D World as they did in the Super Mario Galaxy series, except this time a Flipswitch Panel can be changed between yellow and blue even if the player jumps off and back on it without completely leaving the switch. When all Flipswitch Panels in a series are activated, they turn into green "!" Flipswitch Panels. Making the last Flipswitch Panel yellow gives the player 2000 points. Players can also change the color by tapping on the Flipswitch Panel with the Wii U GamePad.
Flipswitch Panel locations
Super Mario Galaxy
Super Mario Galaxy 2
Super Mario 3D World
Names in other languages