Ah, the issue with the animation editor is different. The animation editor in the current versions of Unity will only edit the internal private state variables (_color) and not the property (color). This is a limitation of the animation editor, and it doesn't help matters that it will "beautify" the member names (_color becomes Color) so it isn't apparent what is happening. The property is what actually changes the color on the sprite, so you don't see any change.
If you want to use the animation editor, you should attach a behaviour similar to this and animate the values of that instead.
using UnityEngine;
using System.Collections;
[ExecuteInEditMode]
public class tk2dAnimationAdapter : MonoBehaviour {
public Color color = Color.white;
tk2dBaseSprite sprite = null;
// Use this for initialization
void Start() {
sprite = GetComponent<tk2dBaseSprite>();
if (sprite != null)
{
sprite.color = color;
}
}
// Update is called once per frame
void Update () {
if (sprite != null && sprite.color != color)
{
sprite.color = color;
}
}
}