"He who marches out of step hears another drum." ~ Ken Kesey
I just did a ton of visors this way. Top color down first, quick flash and then white down last. Came out fine. Truthfully, we have never used the powder and we have never seemed to have issues. Just mix in the Wilflex transfer base to each ink and they seem to work great.
...we sometimes have problems with the powder sticking to the transfer paper after it's run thru the dryer, which makes the unprinted part of the transfer paper stick to the garment.