How to initialize a Color array to a key color, once in code hit frequently.

I'm setting up a color array to use for checking another color variable against it. Since color isn't nullable in Unity, I'm trying to do is initialize it to a key color. (Which is never used in game) From there I set it to the initial value of the color to check against here once, and only once. After that in another method if the two values don't match up I return false. How should I go about replacing the false with an actual value?

Here's the code in question:

 private static Color[] initializePrevColor(Color[] prevColorToCheck, Color[] tileColorToCheck)
     {
         for (int i = 0; i < prevColorToCheck.Length; i++)
         {
             if (false)
             {
                 prevColorToCheck[i] = Color.white;
             }
 
             if (prevColorToCheck[i] != tileColorToCheck[i]
                 && prevColorToCheck[i] == Color.white)
                 prevColorToCheck[i] = tileColorToCheck[i];
         }
         return prevColorToCheck;
     }