Broken highlight color in "Total to sell" SpinBox

When switching from Night mode to Day mode, the higlight color is not updated in the sellTotalBtc SpinBox. The pull request fixes this, you probably just forgot the line...

![screenshot - 02182014 - 11 24 26 pm](https://f.cloud.github.com/assets/3926232/2201403/93f03854-98ee-11e3-96aa-bc5dac937bf1.png)