Custom white balance please

How to white balance on your camera...

You simply aim at something white (really white not just "off white") such as a piece of paper and set the custom white balance in the WB settings area.

You're good to go until your lighting situation changes. If you turn on lights that weren't on when you set the WB, you need to set it again. If you've moved to a new location (e.g. different room--not just a slightly different angle in the same place), you need to set it again.

Basically, all you're doing is telling the camera what white looks like in the current lighting situation. Aperture and exposure times don't influence the WB setting.