The Tricolor File is a World Quest that players will encounter in Enkanomiya. It's part of the overarching World Quest called Collection of Dragons and Snakes, but can be started before the latter.
This World Quest is located in an area unmarked in the World Map. It's a little far and there are no day-night switching mechanisms nearby, so before departing, make sure that your daylight setting is set to Evernight.
Head to the small islet north of the Dainichi Mikoshi. In the area circled in the image above, you'll find a Phase Gate. Approach it to teleport you to point B, which is where the World Quest is located (marked with an exclamation point on the map above).
Once you're there, speak with the afterimage of a Researcher named ???, who you will later learn is named Michiya. She knows that you're after the experimental records, but you finesse your way through with words.
Follow the quest marker deeper into the ruin, where you'll find a clearing with three Elemental Monuments—Cryo, Hydro, and Electro. Lighting up these Monuments will open up the gates with a Vishap of the same Element, which you need to defeat.
Your goal is to find the Bathysmal Vishap Experimental Records, which are located in an Investigation spot inside the Cryo gate. These records are necessary for the Collection of Dragons and Snakes World Quest. While not required, lighting up the other Monuments and defeating the Vishaps will help with completing your Enkanomiya exploration.
Check out our guide on How to complete the Antigonus World Quest in Enkanomiya Genshin Impact to learn more about the secrets hidden in the ancient Enkanomiya.