You can change many view options in your calendar, from the colour of your events, to whether weekends and events that you have declined are shown.
To set your calendar view options:
Click on the Settings cog near the top-right corner of the screen
Choose Settings
Click on View options on the left-hand side of the screen
Set each option as you would like it to appear in your calendar
Click on the Back button in the top-left corner of the screen when complete
To set your calendar colour:
Position the mouse over your name in the My Calendars list on the left-hand side of the screen
Click on the ellipses and choose the colour you wish to use for your events