Problem with Swap Color

Hey guys, I'm working on a swap color feature inside Unity. Though there are some errors that I cannot wrap my head around. You can see in the screenshot here, the 'olderSprite' Scene variables is not found


But on the graph window, I see no red node. Bear in mind that I set the variable on 1 graph and use it on another graph. Though using a Scene variable mean I can use it in different graphs in different game object

Another thing is that, while the function works, it is kind of lagging as you can see in the gif attached
<https://i.imgur.com/xkuDtKf.gifv>

I hope to hear some opinion from you guys