Check this SR-S-064035 in knowledge base.
Here is the excerpt from the knowledge base if you cannot open it up.
"This could be the intended result. Please open the assembly/part and edit the PhotoView Options. Check the contour rendering options. If it is enabled and line color is defined as white, it can give the mentioned results since contour rendering results are seen in the final render only and not in the preview render. Due to this it is only the rendering contour and since contour line color is defined as white it is blending in with the background. Either turn off the contour rendering or change the line color."
In addition, there is another SPR
In addition, there is another SPR# 685264, which talks about PNG output as final image cause the background to be white, therefore, try switching it to output as a JPEG.
Hopefully one of those helps you out,
I've seen that before. I would check to make sure your video card driver is up to date first. If it is just shut it down and bring it back up and see if it does it again.