Suddenly Blonde

So This Game Is Totally Awesome comes out on your NES. And it lives up to its name. You laughed. You cried. You fight the legions of hell and rescue the Damsel in Distress, a cute-looking brunette. And you can't wait for the sequel.

Four years later, it finally arrives - Super This Game Is Totally Awesome is released. And it's even better. The Techno Babble is more babbley, the Slippy-Slidey Ice World is more slippery, the Player Punches are more punchy, and the Damsel in Distress is... blonde? They Changed It, Now It Sucks, right?

Wrong. She was always supposed to be blonde. However, the NES couldn't render blonde hair very well (it was hard to distinguish from skin tone, and they could only have three colors per sprite, making yellow "less useful"), so most artists switched to brown. Likewise, it was impossible to render black hair, because black was generally reserved as the background color.

As consoles became more advanced, some franchise characters kept their quirks as a legacy feature. However, most artists opted to revert to the original concept art. These characters became Suddenly Blonde. This trope refers to any example of a technical limitation that requires a character in-game to differ from their concept art, which is reverted when that limitation is removed. It doesn't just refer to hair color.

Played Straight

 * Pretty much any character with "Princess" in front of her name got reverted to blond hair and a pink dress when those colors became available. Peach and Zelda are the most notable examples, although Zelda has in recent years gone back to brown hair. (It's also worth noting that Peach was originally a redhead, which many people seem to forget.)
 * Also, every princess of Hyrule is named Zelda. There's no reason they should all have the same hair color.
 * Link himself suffered from this trope in A Link to The Past, which is funny since his last two NES games had him with brown hair, which matched the concept art of him. The concept art of Link in Link to the Past still had him with brown/dirty blonde hair, but the in-game sprite of Link has him with pink hair, which is most likely due to palette limitations for the SNES. The GBA port of the game still retained Link's pink hair. All Zelda games after this one kept link with blonde hair afterward (although Twilight Princess dirties it up a bit.)
 * The earliest official art, in Japan, for Peach showed her with her signature blond hair. She was always blond.
 * Same with the Zelda from the first game.
 * Mario and Luigi used to be identical except in color. Nowadays, although the exact measurements change from game to game, Luigi is universally the taller brother.
 * Continuing with Nintendo, Pauline of Donkey Kong was a blonde in cabinet art but a redhead in the actual game. She became a brunette in the second Mario vs. Donkey Kong game.
 * Almost-aversion: Samus Aran took a few games to become fully blond — her second game was in black and white, and in Super Metroid she had a sort of dishwater blond color. Her green hair from the original (after getting the Varia Suit) has yet to make a comeback.
 * Old DOS games that were rendered in EGA color had only 16 colors, so most games made in that era used white, red or gray for skin tone. When VGA came out, most new games (with one exception — see below) took advantage of the new, nigh-unlimited color palette to reinvent the characters of the series. Games which provide examples of this include Duke Nukem, Space Quest, Leisure Suit Larry and King's Quest.
 * The most prominent example of this is Space Quest where Roger goes from a dull brown hair color in his first three games to blonde once he hits VGA.
 * Terra from Final Fantasy VI is blond, but the team was running out of palette space, and the rest of her design worked better if she reused an existing palette. Her palette didn't have enough shades of yellow to create believable blond hair, but they did manage to make believable greenish-blue hair, which is what most fans remember; however, in all of her other appearances (including the official artwork for Final Fantasy VI), she has blond hair.
 * Four of the five playable characters in Final Fantasy V have different hair colors and three of them have radically different hair styles between their official artwork and their in-game sprites. Bartz has light blond/white hair in his artwork, but his sprite has brown hair. Lenna has blond hair worn in a Prim and Proper Bun in her artwork, but her sprite has bright pink hair worn down somewhere between chin and shoulder length. Faris has blond hair worn in a low ponytail in her artwork, but her sprite has purple hair worn in a wild style. Galuf has white hair and is nearly bald with a short mustache in his artwork, but his sprite has a full head and a full beard of brown hair. Krile is the only playable character whose hair in her artwork and sprite match in both color and style with blond hair worn in a high ponytail in both.
 * The qunari from the Dragon Age universe were originally supposed to have horns, but because they had issues making the helmets work over horned characters, that was dropped in the first game. The second game is coming out soon, and lo and behold, the qunari suddenly have horns. Opinions vary on if the horned version is as good as the model the first game used.
 * To their credit, Bioware has explained why the qunari characters in the first game don't have horns. Sten was a special case who was born without horns, while all others removed their horns to show their social status.
 * The elves in Origins looked like short, somewhat skinny humans with pointy ears. In Dragon Age 2, they have also recieved some more distinguishing facial features, like large eyes and a flat transition from forehead to nose, which makes them look like small, white Na'vi.
 * Happens all the time in World of Warcraft. The best-known example is Dark Lady Sylvanas, leader of the Forsaken Undead and a High Elf. But since High/Blood Elves weren't in the game until the first expansion, she had a Night Elf's model instead (which looked nothing like her appearance in Warcraft 3). It wasn't until the second expansion that she was not only made a proper High Elf, but became one of the very few characters in the game whose model was actually unique.
 * Space Quest's hero Roger Wilco. Brown-haired in his first three adventures, at least dirty blonde as of Space Quest IV, also looking rather bleached in both Space Quest V and the Space Quest I remake.
 * The 1987 Famicom Star Wars game gave Luke Skywalker black hair except in cutscenes.
 * In Antarctic Adventure and Penguin Adventure, Pentarou's skin was jet-black, though he was already blue on some box covers and is definitely blue in other games even on the MSX.

Notable Aversions ("legacy features")

 * The brothers Mario had appearances designed to be easy to render on the NES — the caps were to avoid having visible hair, the overalls were to make the arms more distinct, and the mustaches were to make the lack of any visible mouths less noticeable. This also had the side effect of making the characters look distinct during an era where almost every video game hero was either a cute ball-like monster or a Japanese boy with blue, spiky hair.
 * In Metroid II, since they didn't have color available, the artists put large, noticeable shoulder pads on the Varia Suit to make the difference obvious. The Varia suit is now dark orange (with Samus' regular suit being yellow), but the shoulder pads have remained, and actually became notably bigger in Metroid Prime.
 * As mentioned above, EGA games tended to use white or red for skin tone, and Commander Keen was no exception. However, while the last few games used VGA color, which had no such limitations, Keen still retained completely white skin. It's especially noticeable when a giant drawing of him is shown on the title screen of the fourth and fifth games (the "Goodbye, Galaxy!" arc).