Canon PowerShot A580 2463B020 User Guide (en)

You are recommended to set the shooting mode to 
the exposure compensation setting to [±0] before setting a 
custom white balance. The correct white balance may not 
be obtained when the exposure setting is incorrect (image 
appears completely black or white).
Shoot with the same settings as when reading the white 
balance data. If the settings differ, the optimal white 
balance may not be set. In particular, the following should 
not be changed.
- ISO speed
- Flash:
Setting the flash to 
 is recommended. If the 
flash fires when reading the white balance data with the 
flash set to 
, make sure that you also use the flash 
when you shoot.
The white balance data is retained even after the camera 
power is turned off.