You can install our site as a web app on your iOS device by utilizing the Add to Home Screen feature in Safari. Please see this thread for more details on this.
Note: This feature may not be available in some browsers.
Unfortunately not - at least in this version of the software. Who knows what v11 will bring. Right now it's only light or dark depending on day or night.
You can change it manually to a dark background by changing the Display Mode. FTM...
Display Mode: Customize the DAY (light background) or NIGHT (dark background) setting of the touchscreen. When set to AUTO, the brightness changes automatically between day and night brightness based on ambient lighting conditions.