I just picked up a case of 15w-50 AeroShell yesterday and noticed the bottles were red. The website indicates all AeroShell will be in red bottles going forward. It seems that they would have put the piston engine oils in one color and turbine engine oil in another to make them stand out visually. Here's the link to the change: http://www.shell.com/global/products-ser...l#textwithimage