Google Calendar now automatically dims the brightness of past events by default. Google says this new shading feature is designed to “help you focus on what's next.”
The new feature seems to make calendar navigation easier and upcoming events stand out, but it’s pretty easy to turn off if you don’t it.
To turn dimming and graying off, you can either click on the down arrow to the right of “My Calendars” under the small calendar on the left side and select Settings, or click on the gear icon on the top right in Google's navigation bar and choose Calendar Settings.
This takes you to the Calendar Setting page. Scroll down to event dimming and uncheck the box, and your calendar will no longer be dimmed.
Google also has an option in here to dim future recurring events.