If you've ever viewed multiple calendars in one view in Outlook Online, you know how useful it is, but also how confusing it can be. Use colors and charms to know at a glance which appointment belongs to which agenda.
Outlook can display different calendars in addition to your default calendar. Additional calendars you have created yourself, shared calendars from other people, calendars from groups you belong to, and calendars from Planner can all be viewed individually or together.
When you view multiple calendars together, it is easy to get a little lost. Microsoft has made it easy to distinguish between different calendars by using colors, and you can also add charms (icons for each appointment) as default for each calendar and separately for specific events.
Your default calendar shows appointments in blue, without charms.
To see even more calendars, click it in the sidebar on the left so that a check mark appears. 
The appointments from those calendars appear in the calendar view. Outlook gives them a different color by default.
In our example, two of the events have an icon – called a charm – that is already assigned to
This is done automatically by Outlook when it finds a word that matches a charm. The green appointment has a charming birthday cake because the title of the appointment & # 39; Mike & # 39; s birthday & # 39; is. The red appointment has a pen and paper charm because the appointment contains the word & # 39; tutorial & # 39; contains. Other terms that cause a charm to be added automatically include & # 39; dentist & # 39 ;, & # 39; doctor & # 39 ;, & # 39; vacation & # 39; and & # 39; car & # 39 ;.
You can manually change the default color for a calendar by clicking the three dots next to the calendar in the sidebar and then select the "Color" option.
Select the desired color and the appointments on the calendar will immediately change to match.
You can also add a standard charm to a calendar, which will be applied to every appointment in that calendar. Click on the three dots next to the calendar in the sidebar and then select the "Charm" button.
Choose the charm you want, and the appointments will immediately change to match. 
One of the appointments we mentioned earlier still has the pen and paper charm that Outlook has automatically applied.
The previous automatic charm overrides the default of the calendar, but you can change it. Double-click the appointment to open it, then select the charm.
This opens the charm box. You can choose any charm you want, but to match the default charm for the calendar you need to remove the automatically applied charm. Click on the circle at the top left.
This removes the custom charm and the appointment retrieves the default charm you selected for the calendar.
If you don't want to apply a standard charm to a calendar, but you want to apply custom charms to specific appointments, the process is similar. Double-click an appointment to open it and click the circle next to the appointment title.
Opens the charm box. Choose the desired charm and click on it to apply it to the appointment.
Close the appointment and the charm is visible about the appointment in the calendar.
Currently it is not possible to add your own colors or charms to Outlook, so you must use the options that the company offers you. However, there are enough colors and charms that you can create unique markings for quite a few calendars in most situations, which is certainly better than when multiple identical calendars stare back at you.