Adjust GUI colors to match terminal colors

![seoul256-old](https://cloud.githubusercontent.com/assets/700826/5153034/32d59042-7254-11e4-926d-003cbc9ba42c.png)
![seoul256-new](https://cloud.githubusercontent.com/assets/700826/5153032/31f307f4-7254-11e4-90c5-ee22875b20e6.png)

![seoul256-light-old](https://cloud.githubusercontent.com/assets/700826/5153033/31f38760-7254-11e4-853c-b53f49fda451.png)
![seoul256-light-new](https://cloud.githubusercontent.com/assets/700826/5153031/31edd040-7254-11e4-942b-667b12796c35.png)