Not sure if there would be much difference across the different colours of wyandotte, but I ended up with a white sport wyandotte who I was positive was a roo based on this thinking - it was a a good 2-3 weeks behind my other chicks on the feathering but at around 6-7 weeks she was fully feathered out and looking a hell of a lot more like a hen than a roo, so I stuck her photo up and 9/9 people told me 'he' was indeed a she!
From the research I've done, the feathering theory is generally true, but some lines and I suppose some cases its the opposite!
My wyandottes a few of the females did feather in faster but a few did not. The males all had thicker legs and became much bigger with larger red combs and wattles than the females by about 6 to 8 weeks it was apparent who was who so you don't have to wait long to figure it out. Plus watch their additive the Roos will become much more feisty usually.