You can choose one of the predefined color schemes from the drop-down list on the right pane and use it off the shelf. You can install more color schemes from $website$
Apart from that you can adjust your chosen scheme as you wish. For this purpose you have all the settings in the tabs on the left pane. Any changes you would have made will be immediately applied but only on the popup so you can safely play with it.
Apply
button on the right pane.
If you want to set up current settings as a
default settings for all websites press
Set as default
button on the right pane.
You can find more help on the support forum, read existing tutorials or ask a new question.