fix: convert calculateColor to arrow function

[OnlineBunker]

Refactored calculateColor function to use an arrow function

• Ensures it’s defined before use
• Prevents potential hoisting issues
• Improves clarity and maintainability

[Copilot]

Pull request overview

This PR fixes a bug where calculateColor was declared as an implicit global variable by adding the const keyword to properly scope the arrow function declaration.

• Adds const declaration to calculateColor arrow function to prevent creating an implicit global variable
• Ensures proper lexical scoping and best practices for function declarations

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