Nested Classes

NestedClassHolder.cs

// Use a class that does not inherit from MonoBehaviour and has attribute [System.Serializable] 
// then reference that in a MonoBehaviour class. This results in a dropdown in the Inspector 
// for the referenced class.
// The documentation says to have the NestedClass inherit from System.Object but I've seen no need for that.
// For more robust functionality, consider creating a ScriptableObject/template for the Nested Classes,
// then reference those. It won't drop down in the inspector the same way, but it affords other benefits.

using UnityEngine;
public class NestedClassHolder : MonoBehaviour
{
    public NestedClass1 nestedClass1;
}

[System.Serializable]
public class NestedClass1
{
    public float myFloat = 5.5f;
    public Color myColor = Color.blue;
}

Alternative setup:

public class Class : MonoBehaviour
{
   [System.Serializable]
   public class NestedClass
   {
             public float data;
   }
 
   public NestedClass data = new NestedClass() ;
};

I'm not sure when this method would be preferable.