Blues:
Are a color with associations of cleanliness, of water and washing and flushing dirt away. There was a time when such nuances were important to manufacturers; the bean-counters didn't rule the way they do now.
By tinting the vinyl blue, a subconscious message was sent: This is an appliance that creates cleanliness. Everything touching your dishes is clean. Things washed in it will be really, really clean.
White also has associations of cleanliness, but I think too much of it makes things look "blah" - a point you can prove to yourself with a single visit to a big-box store carrying new appliances. You can hardly tell the BOL stuff from the so-called "best."
To give you an idea of how powerful the subliminal message of blue was, look back at '50s dishwashers, many of which had racks in other colors, like pink and red. By the '60s, nearly every manufacturer had moved over to blue or a variation. The message obviously had great sales value.