From the Super Mario Wiki
Blue Spaces are spaces in the Mario Party series that provide coins (three to nine, depending on the game and specific circumstances) to characters who land upon them. They appear in every Mario Party game, and they are the most common spaces in the series. These spaces can vary in hue and shape, depending on the game. In Mario Party 5, they are known as Plus Spaces. In Mario Party Island Tour, they have a much different role. Known as Safe Spaces, they protect the player from getting hit by the Banzai Bill in Banzai Bill's Mad Mountain.
In New Super Mario Bros., there are also Blue Spaces, but they are different than those in the Mario Party series. The Blue Spaces represent levels that have been completed by Mario or Luigi. New Super Mario Bros. Wii and New Super Mario Bros. 2 also have Blue Spaces, which serve the same function. Levels that have yet to be beaten or that have been beaten through the use of the Super Guide feature (New Super Mario Bros. Wii only) are represented on the world map by Red Spaces. These also return in New Super Mario Bros. U, as well as New Super Luigi U, sharing the same function.
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