i have the 4700k no yellow at all. used to be pure white when i first got them, now after burn it it looks JUST like a newer bmw (i have compaired lights). i love these things.
As for mazda 6..the housing is rated for hids but since we are american spec we lost allmost half the options of our atenza counterparts. I have 4100 catz and they are real nice...they look blue for the 1st 8 seconds then turn white. With my properly aimed hids nobody cuts me off at night the housing of the 6 will also reflect up so don't stare down at the housing too long.
I got my Polarion Philips 4100K HID kit from XenonExpert (www.xenonexpert.com). He's a moderator on Mazda3forums and he's offers great customer service.