Luigi is very similar to his older brother in appearance, although Luigi is slimmer and taller. His face is noticeably thinner and chinless, and his hair is the same style as Mario's, but more of a dark maroon. Luigi's mustache is dark brown and smooth, and each half tilts slightly upward. He has light blue eyes like his brother, but appear more oval shaped.
Luigi also wears clothes similar to Mario, but his shirt is green instead of red. Layered over the shirt is unfaded dark denim jean overalls which reach to above his ankles. He also has dark brown work shoes with tan bottoms that reach above his ankles; Luigi's overalls and shoes are darker than Mario's overalls and shoes. Luigi's Cap is similar to Mario's Cap, being green instead of red and having an "L" replace Mario's signature "M." Artwork for the Mario & Luigi series has consistently depicted Luigi as wearing red and white striped socks that resemble candy canes; this trait is not present in any other games.
Mario and Luigi's color preferences are reflected throughout the land in the form of various enemies, such as Koopa Troopas and Cheep-Cheeps, who also come in red and green varieties. These foes even reflect the brothers' personalities, with red ones being more aggressive and green ones acting cautious. In fact, Mario and Luigi are not the only known red and green brothers, with similarly color-coded siblings including Cork and Cask, the Red and Green Bridgemasters, the Armored Harriers, Massif Bros., Elder & Junior Shrooboid and Gigi and Merri. When tattling the younger of the Armored Harriers, Goombella theorizes that it may be some sort of rule that younger brothers must wear green, offering a possible explanation for Luigi's trademark green shirt and hat.
However, Luigi has not always chosen to wear his usual green and blue clothes. Mario Bros. originally dressed Luigi in a black shirt and green overalls, although artwork showed his shirt to be red. Shigeru Miyamoto stated that the green color of clothing for Luigi was inspired by the enemy Shellcreeper. Wrecking Crew gave him a magenta pair of overalls and helmet, seemingly leaving him shirtless. Even Super Mario Bros. gave its Luigi a green shirt and white overalls (although Super Mario Bros. Deluxe replaced this with a less aberrant brown shirt and green overalls, leaving his original colors to Fire Luigi, who usually has an inverse scheme), even though his usual palette and appearance had emerged in artwork.
Luigi was initially rather infamous for being a palette swap of Mario in his earlier adventures. This applies to Mario Bros., Wrecking Crew, Super Mario Bros., Super Mario Bros. 3, Super Mario World, Super Mario World 2: Yoshi's Island, and even the rare solo quest that is in Mario is Missing!. Luigi's first unique sprites came in Super Mario Bros. 2, in which his artwork appearance conveniently coincided with the tall Mama's sprite. Nintendo of Japan would not adapt Luigi's artwork differences to his in-game sprite until Super Mario Kart, although Luigi's various models have been unique almost ever since, even in remakes of games where he was originally a palette swap (such as Super Mario All-Stars, Super Mario All-Stars + Super Mario World, Super Mario Advance 2, and Super Mario Advance 4).
Both Mario and Luigi have been described as "cutesy," to the extent that Shigeru Miyamoto considered redesigning them to "become a bit more grown-up" in the GameCube era, for instance by removing their trademark V sign. However, aside from growing more realistic as graphics have advanced, Luigi and his brother have changed little over the years, and continue to flash the V sign regularly.
Luigi's appearance does, however, tend to lend itself to heavy stylization. The Luigi's Mansion graphical team took it upon themselves to animate every part of Luigi to convey emotion, resulting in such exaggerations to the plumber's body as head-expanding screams during boss cutscenes and complete flattenings by fake doors. The Super Smash Bros. series applies Luigi's cowardice to his actions, making most of his attacks look reckless and unwilling and giving him awkward movements, securing his official title as the series' "dreamy, comical poster boy."