Go to Enhancements and set the Internal Resolution to 2x (720p) or 3x (1080p) to sharpen the 3D models.
Double-click the main Dolphin window and select the folder where your Pokémon Colosseum ISO file is stored. Pokemon Colosseum Game Pc
Select Vulkan or Direct3D 11 for the best performance on most modern PCs. Go to Enhancements and set the Internal Resolution