The 90° Reflectors are designed to give wide, even umbrella coverage (no hot spot), and excellent at close flashtube-to-umbrella distance.
White allows virtually no light to pass through it and makes a very efficient bounce umbrella. It is glossy white and gives similar output to a silver umbrella without the harshness.
Translucent umbrellas can either be used to shoot through or to bounce the light. The difference in light output between shooting through and bouncing is very small. The material is neutral and allows about 50% transmission.