White balance from a grey card

Hi Stephen (I hope I have that right).

Are you asking how to use a grey card, or how to set the (so-called) White Balance in Aperture?

Here is a good article on the use of neutral references to set the color cast. Pay particular attention to the section "Custom White Balance: Choosing A Neutral Reference".

Here is the page from the Aperture User Manual on setting the White Balance.

HTH,

—Kirby.

Ah ... use Lift & Stamp.

White Balance is an adjustment. Adjustments are copied from one Image to others by lifting them (they show in the Lift & Stamp HUD) from the source Image, selecting target Images, and stamping. Note that lifting lifts all adjustments (and can also lift metadata). You can remove adjustments and metadata from the Lift & Stamp HUD before stamping Images.

I use the keyboard shortcuts ⌥⌘c to lift, and ⌥⌘v to stamp — but these may not be the defaults. Full information on using the Lift & Stamp feature is here in the User Manual.

Note the commands at the bottom of the Metadata menu. You should have three options for lifting: adjustments, metadata, and adjustments and metadata together. Your currently-assigned keyboard shortcuts show at the end of the line in the menu showing the name of the command.

—Kirby.