If your organization is using specific color theme for Office documents/ templates. You can change the default color theme using built-in Excel ribbon Commands. Unprotect the sheets before applying the theme colors. And then Go to  ‘Page Layout’ Ribbon Menu and use the commands in the Themes Group. Please see the step by step instructions below:

Unprotect all sheet:

We need to un-protect all worksheets before applying the color themes. Please follow the below steps to un-protect all sheets:

Unprotect Dashboard Sheets

1. Go to Settings
2. Go to Dashboards Section
3. Turn OFF Dashboard Protection
4. Apply Settings

Unhide Index Sheet

1. Go to Navigation Section
2. Change Navigation Type to Index
3. Apply Settings

Unprotect Settings sheet:

1. Now go to Review Tab
2. Click on Unprotect sheet
3. Enter Password AT_AUPMS

Now, we have unprotected Dashboard and Settings sheet.

Unprotect Main Home Sheet

• Now Click on the Back to Main sheet to Go to Home Sheet .
• And Unprotect Home Sheet from the review ribbon tab using Password AT_AUPMS

Unprotect Help Sheet

• Go to Help Sheet using the worksheet tabs
• And Unprotect Home Sheet from the review ribbon tab using Password AT_AUPMS

Now Excel allows to make the theme changes:

Changing theme Colors

1. Go to Page Layout Ribbon menu tab
2. Click on colors command from Themes Group
3. Choose the Styles of your Organization