The title screen in the brown colors
Pokémon Brown Mode is a specific Glitch Dimension in Pokémon Yellow that allows the player to play Pokémon Yellow in brown colors.
It exploits how Trainer class 0xFF (not to be confused with ゥ, A (0x37) who can be encountered with the Ditto trick and a Special stat of 255) causes a battle to restart in Victory Road. When the battle is repeated from a Lorelei battle in Game Boy Color mode seven times, the game will reset in brown colors just before battle. From then on the glitch cannot be repeated until a normal reset is performed (returning the game back to normal colors).
Though the effects of this glitch are mainly just on how the game is displayed, it does enable some glitchy transitions when the screen is refreshed at certain points such as closing the Pokémon menu, and also allows the player to be able to disable the darkness from Rock Tunnel.
In order to do this you must first be playing on Game Boy Color mode. This will not work on Super Game Boy or monochrome Game Boy mode (the glitch involving the battle restarting will work differently).
Due to the very specific nature of the glitch, this may not work on some emulators (although it does work on BGB). Luckily it is also confirmed on a physical Game Boy Advance SP as well as Nintendo 3DS Virtual Console.
1. Prepare ws m (0x63) with a bootstrap code (this one is recommended:)
2. Prepare the following items in the bag:
Item 3: Lemonade x255
Item 4: Carbos x208
Item 5: X Accuracy x48
Item 6: Poké Ball x119
(This changes D030 (responsible for enemy Trainer AI and speech) to unused Trainer 0xFF (not to be confused with Trainer 0x37 who is accessible with the Ditto trick and a Special stat of 255). The AI causes the battle to restart, possibly corrupting the stack each time.)
(if your bootstrap code doesn't redirect to item 3 and goes to somewhere like item 2 instead, set up the items code from there)
3. Go to the Pokémon League and fight Lorelei (you must fight Lorelei, other Trainers likely won't work).
4. Use ws m 7 times. On the seventh battle the game should reset into the brown Glitch Dimension.