Are you asking about metering or white balance. I think the latter. Yes, you can set a custom white balance based on a gray/white card reading. The instructions are on pages 52-53 in the K-3 user manual, though they are a little confusing. Let me see if I can provide the steps in a clearer fashion:
- Make sure rear LCD display is enabled and not turned off
- Press ◄ on the 4-way controller to go to white balance control
- Choose "Manual White Balance" (2nd from right...strange icon...box with two arrows below) and press ▼ to move down to icon1, icon2, or icon3. These are three possible manual presets. The rear LCD should provide a live view display.
- Point the camera at your white card and fully depress the shutter. The display should refresh with the white balance based on your white card.
- You can use the arrows to fine tune the position for the reading. You can also push the "info" button to manually fine tune the set point.
- Push "OK" to assign that value to the preset
Give it a try in the comfort of your living room to make sure you're a comfortable with the process. Have fun at the game!
Steve