What the viewfinder indicators mean on a PowerShot SD series cameras.

The indicators light or blink when the <ON/OFF> button or the shutter button is pressed.
Upper Indicator
Green: Ready to shoot / Ready to communicate (during a computer connection)
Blinking Green: Starting up / Recording to SD card / Reading SD card / Erasing from SD card /Transmitting data (during a computer connection)
Orange: Ready to shoot (flash on)
Blinking Orange: Ready to shoot (camera shake warning)
Lower Indicator
Yellow: Macro mode / Manual focus mode
Flashing Yellow: Focusing difficulty (although you can press the shutter button, try using focus lock or AF lock).