Hi,
I cannot find a default teal theme color, either. You can try creating a custom theme color to use teal, accent 4 color. See Change
a theme and make it the default in Word or Excel for detailed steps.
If you only want to change the page border color to teal, you can try the following steps:
1. Open the Word document you want to change the border color for.
2. Click Design tab, click Page Borders button in the
Page Background group.
3. In the opened dialog box, click Color drop-down menu.
4. Click More Colors.
5. Click Custom tab.
6. Under the RGB color model, modify the value like below:

7. Click OK. Click OK again.
Hope this helps.
Regards,
Steve Fan
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