In "Star Wars Jedi: Fallen Order," the Journey Plus mode allows players to replay the game with their progress and unlocks. While the game offers various lightsaber colors, your ability to wield a specific color in Journey Plus can depend on your choices and collectibles from the main campaign.
In Journey Plus, you can choose the color of your lightsaber, including red. However, in specific scenes, such as the moment in which you face Cere and use a red lightsaber, the game may restrict you to that color to maintain narrative cohesion at that moment. Otherwise, you can usually switch to any previously unlocked lightsaber color during your journey.
To ensure you're getting the most up-to-date information or additional contexts, you might want to check community discussions or updates from the game's developers, as details may change with patches or additional content.