Possible No 4 engine explanation is that all 4 engines are pulled back to idle after reverser stowage in an RTO.
If No 4 was a recently replaced engine it would have a freshly painted nose spinner spiral and there would be little blurring at idle.
The other engines could have been on wing long enough to erode away the spinner paint.
I'm not sure that this is the explanation for this photo since other scenarios could apply, e.g. # 4 brought to idle to control yaw while others left at higher power.
Of course I don't have a suitable explanation for why the reversers are not seen to be deployed at this point.
Just a interesting fun puzzle seeing how mixed up you can get trying to read a photo.
