Kolorado is a " Indiana Jones" type character with a British accent. He's originally from Koopa Village, but spends must of his time looking for treasure across the Mushroom Kingdom.
We first meet Kolorado In the "Dry Dry Dessert." Kolorado is searching for the Dry Dry Ruins, and the rumored treasures left behind. During the game Mario uncovers and explores the Ruins and gives Kolorado an artifact he found there. Kolorado eagerly trades for the artifact, and eventually finds the ruins for himself. He then takes all the credit for the find, and continues his quest for treasure and adventure.
He later teams up with Mario on a trip to Lavalava Island, once again in search of treasure. His foolhardily attitude causes him to fall into several dangerous situations in which Mario must rescue him. Eventually Mario finds the treasure Kolorado was looking for and trades it to Kolorado for a seed that Mario needs for his quest. After this find, Kolorado returns back to Koopa Village and to his wife.
During the epilogue of the game we see Kolorado leading an expedition to the Crystal Palace; a fabled castle in the snow which Mario visited during his quest. The expedition is cut short when he receives an angry letter from his wife, forcing him to return home.
Paper Mario: The Thousand Year Door
Kolorado is mentioned during a side quest in the sequel to Paper Mario; Paper Mario: The Thousand Year Door
. It is read that he returned to Dry Dry Desert, and helped a character named Lumpy find oil.