P67-C43 Motherboard (Enabling Dual-Channel RAM)

[A49ER08]

Hey, I have a P67-C43 mobo and I recently purchased G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) RAM.
Unfortuantely the sticks won't dual-channel.. am I doing something wrong? I've tried placing them in different slots... I'm not sure what I'm doing wrong.
theres 4 DDR3 Slots
DIMM_1 (blue)
DIMM_2 (black)
DIMM_3 (blue)
DIMM_4 (black)

 

[NovJoe]

Place them in 1 + 3 or 2 + 4 and you'll get Dual Channel automatically.