The only situation I can imagine a driver not noticing a huge truck perpendicular to them on the highway, regardless of what color it is, is that they're not paying any attention at all.
The optical distortions that cause road surface mirages could well entirely hide another vehicle. In this case, since the trailer was painted white, only the wheels and lower chassis would need to be hidden for the image to become unrecognizable. Not saying that's what happened in this case, but there are situations when your forward vision could be compromised. (There is a theory that the colder ocean may have caused a similar optical phenomenon and hidden the iceberg that sunk the Titanic.)
The optical distortions that cause road surface mirages could well entirely hide another vehicle. In this case, since the trailer was painted white, only the wheels and lower chassis would need to be hidden for the image to become unrecognizable. Not saying that's what happened in this case, but there are situations when your forward vision could be compromised. (There is a theory that the colder ocean may have caused a similar optical phenomenon and hidden the iceberg that sunk the Titanic.)