Theory: Blue and Yellow Toad are in the Baseball Games

Abstract
The distinct characters Blue Toad and Yellow Toad were part of the group of five Toads present during Mario Superstar Baseball, and Mario Super Sluggers.

Arguments

 * Argument 1: In the two Baseball games, the Toad palette swaps are referred to by their names: Red Toad, Blue Toad, Yellow Toad, Green Toad, and Purple Toad. We know these represent character names and not colors because, in the same game, Yoshi is not referred to as Green Yoshi. This means that the names of the characters featured there are in fact Yellow Toad and Blue Toad.


 * Debunked Counterargument 1: In Mario Superstar Baseball alone, the Red Toad is referred to as simply Toad, despite not being the main Toad due to his red vest. However, every character from Mario Superstar Baseball returned in Mario Super Sluggers, but only Red Toad had a name change- going from Toad to Red Toad. The same did not happen to characters like Shy Guy, Yoshi, or Koopa Troopa, despite that it could have. This seems to imply a retcon in this case.


 * Debunked Counterargument 2: Supposedly, Yellow Toad and Yellow Toad of the Toad Brigade share a name and appearance, just like the Yellow Toad in Mario Superstar Baseball and New Super Mario Bros. Wii, which despite being provably separate characters. However, Brigade Yellow Toad appears to have no canon source for ever being referred to by the name Yellow Toad, and he also appears to go unnamed in Japanese. There also appears to be no source for Hint Toad ever being called Blue Toad before Super Mario Odyssey, either, and the same applies to Bank Toad being called Green Toad before Super Mario Galaxy 2. With that, no provably different Toads have ever shared a name and appearance.


 * Argument 2: The personalities and jobs of the characters seem to match. We see in games like Super Mario 3D Land and the New Super Mario Bros. series that the Toads are brave for their species and devout servants of Peach, and a description from the European website for New Super Mario Bros. Wii calls them “loyal servants to the Mushroom Kingdom throne”. This matches their roles and personalities in the Baseball games and Sunshine. In Mario Super Sluggers, for example, Blue Toad guards an area for Peach and hides a statue for her, and assists her when she comes to ask. This also matches games like Luigi’s Mansion 3, where the Toads carry Peach’s luggage and accompany her on vacation.


 * Debunked Counterargument 3: Yellow Toad’s personality in Mario Super Sluggers does not match as closely as Blue Toad’s does. He appears to prioritize his own safety over helping Peach defeat Bowser Jr. However, when defeated, he gets over this quickly and goes to help Peach, saying “wherever you lead, Princess, I will follow!” Either way, Yellow Toad joins Peach’s baseball team prior to the events of the earlier Mario Superstar Baseball, implying he has been convinced to help before, and this last line may have carried over to future games.


 * Argument 3: In the opening to Luigi’s Mansion 3, Blue Toad is seen tossing a baseball to himself, linking Blue Toad to baseball. Elsewhere in Luigi’s Mansion 3, main Toad is seen with golfing equipment, and he was directly playable in a golf game- this could also apply to Blue Toad. None of the other possessions brought by the Toads hint at any potential spinoff connections.