I always have a problem of yellow cast on my photo when using external flash. I'm using 420ex and bouncing to celing without bounce card. Is it due to flash is yellowish or light bouncing problem? Before buying this flash, I've tried with a third party flash, think it's sigma and photo seems whiter. But that time during testing, I thought that photo looks washed out, thus chosen 420 instead. Anyone can advise how can I eliminate the yellow cast with external flash?