Is there any way to change the Calendar app colors of my Nexus 5?
If you want something different for your Calendar app, provide it a new look, want a brighter moos, or anything you are up to, you can try the app "Set Calendar Colors" from One Rainboot Studios, in the Play store, without rooting access.
This app works great to be able to change color of Google calendar and the Outlook exchange calendar. It should be able to modify others as well. All you have to do is selecting the calendar, and a color picker helps you to select your color. If you insisted, you can automatically synchronize your calendar colors to your Google calendar web app.
You can also backup and restore your colors after a factory reset.
And itís free.
Open Calendar, tap menu and then Settings, then tap your Google account email address. You'll see a list of all of your calendars with a color box to the left of each. Tap the color box, then choose your new color!