Because a lot of users don't like the way 'today' is highlighted in the calendar in Outlook. this is a fairly common question:

Is there any way to make “today” standout in the monthly calendar view? It’s difficult to see it with all of the colors swirling around.

While you can’t change the 'today' highlight, you can use color categories or conditional formatting to help highlight the current date. Even changing the calendar color can help. They aren't perfect solutions, but may be better than the current highlight.

If you don't use color categories, use conditional formatting to highlight the events for today in a bright color. However, conditional formatting won't work if you use color categories on your appointments, as color categories override conditional formatting.

Another option is an all-day event that you move to the current day, each day. It has a color category assigned and is set as Busy so category color shades the entire cell. This works best if your calendar doesn’t have a lot of appointments as it takes up space on the already-small calendar grid. Because he event is marked busy, it may not the best solution for a work account where co-workers need to see your free/busy (you'll always be busy).

Another, similar option is an all-day event for previous days, with a black category assigned to mark off days, much like you’d do on a paper calendar. Or use conditional formatting to color all uncategorized past appointments black.

For a different take on it, you could use a custom view to hide old appointments. Today would be the first date with appointments visible. The filter conditions would be Start date is on or after today.

Change Calendar Color

Although you can't change the color of the line, a different calendar color might help. I think pink stands out the best, but any color except gray or yellow is more visible.

Change the Calendar color:

1. Select the calendar.
2. Right-click on the calendar folder and choose Color .
3. Select a different color.

Or

Color on the View ribbon and select a different color.

Use Conditional Formatting

If you aren't color categorizing most of your appointments, you can create a conditional filter to change the appointment colors. When appointment colors don't match the calendar color, the day highlight stands out (a tiny bit) better. If you aren't using a lot of recurring or multi-day appointments or meetings, you can highlight appointments that start today (see screenshot at the end of this article).

You can create multiple conditional formatting rules to color-code appointments instead of using categories.

To create a conditional formatting rule:

1. Switch to the View tab and click View Settings (on far left)
2. Click Conditional formatting button
   
3. Click Add and name your rule.
4. Choose a light color. (Unfortunately there isn't an option for White, 'none' is transparent.)
   
5. Click the Ok button to Save and close the conditional formatting rule. A warning dialog will tell you the rule will be applied to all events. Click Ok.
6. Because just changing the appointment colors is usually not enough to highlight Today, you can create a second Conditional formatting rule, using the Advanced tab to set a filter for Start Today and Recurring equals no. Note: If you don’t use Recurring equals no (or Recurrence pattern is empty), all recurring events will be highlighted. (This rule is less useful if you have a lot of recurring or multi-day appointments or meetings as few appointments will be highlighted 'today'.)
   
7. Select the Today rule and click Move Up to make it the first rule in the list. (The rules are applied in order, with the first rule overriding subsequent rules.)
   
8. Click OK 3 times to return to Outlook.

Any appointment or event that is not assigned a color will be colorized by the conditional formatting rules. A white or a lighter gray color would blend into the background better but the contrasting colors helps the bar stand out.

After creating the conditional formatting rule and applying it to your view, go to the View tab, Change View and select Save View as a new view. This way, if your current view gets reset, you'll have a copy of the view to re-apply.

Sample Screenshots

These screenshots are examples of using a view to color or hide past events. the first screenshot is with no filters set.

This view hides past events that are not recurring.

This view colors past events that are not recurring.

Today is highlighted:

The filter dialog for a conditional format to shade past events:

The filter you'll use to hide past events: