Chance were always experimenting and these oddities can often be test pieces. The 'correct' way is white, light colour, dark colour, so this one is very odd.
As they were silk-screen printed, it could just have been someone using the wrong enamel at the wrong time!
With respect to the Cordon vase: it is possible these was enamel sprayed rather than silk-screened, which doesn't allow printing to the edge. Difficult to tell the difference, but if you use a magnifying lgass you may just detect a slight texture of a regular pattern (the screen). Sprayed vases would not have any definable pattern.
However, if the white portion is smooth as a babies botty, then you're looking at opal glass (very rare) - see Nic's topic...http://www.glassmessages.com/index.php/topic,6869.0.html
This vase is rare on three counts: opal glass, no pattern and 8" tall :shock: