I have raised chinese and african geese for several years and the coloration doesn't inicate sex at all. The white chinese are male and female. Also the africans successfully interbreed with the chinese and create offspring that can look like either breed or a mixup of the two. Best way to determine sex by casual observation is by their behavior in the spring mating season.

With Mature Chinese geese the knob will be slightly larger on the male.

Color has nothing to do with it.