Do you know if there is a on the Touch shield ?
I want to know that because I'm using the Touch Shield on a Seeeduino board and when we don't use the device it's useless to consume the power.
The backlight is always default on, if you want to change the backlight, you need to do some hacking on the board. Please look at the back side of the board. There's a BACKLIGHT label. One side is named as ON, and the other side is named D7. We need to cut the wire between middle pad and ON pad, solder middle pad with D7 pad. As shown below.
Then you can control the backlight via D7.
To open backlight: digitalWrite(7, HIGH);
To close backlight: digitaWrite(7, LOW);