Fade emission color using standard shader

I'm trying to fade between emission colors. My problem is that the emission color is set exactly once. After that the script won't change the emission color again. I checked the debugger and the color object is changing correctly. Only the rendered emission color is incorrect.

 void Update ()
 {
     // ... more code ...
 
     float t = Mathf.PingPong(Time.time, slowFlashInterval);
     currentColor = Color.Lerp(Color.black, flashColor, t);
     body.GetComponent<Renderer>().material.SetColor("_EmissionColor", currentColor);
     body.GetComponent<Renderer>().material.EnableKeyword("_EMISSION");
     
     // ... more code ...
 }