Default Office theme: registry value default ui theme (HKCU common)UserHKCU\software\policies\microsoft\office\16.0\common

Policy ID: L_DefaultUIThemeUser
Scope: User Configuration
Supported on: At least Windows Server 2008 R2 or Windows 7
Source: Microsoft 365 Apps / Office Administrative Templates (version 5568.1000)
Category: Microsoft Office 2016 › Global Options › Customize

Registry

default ui theme

REG_DWORDUser

HKCU\software\policies\microsoft\office\16.0\common Current key

Enabled value: Depends on the option value
Element: Theme:

Options
Item	Stored value
Colorful	0
Dark Gray	3
Black	4
White	5

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\common]

; Options (use only one)
; Colorful
"default ui theme"=dword:00000000
; Dark Gray
"default ui theme"=dword:00000003
; Black
"default ui theme"=dword:00000004
; White
"default ui theme"=dword:00000005

CMD

:: Options (use only one)

:: Colorful
reg add "HKCU\software\policies\microsoft\office\16.0\common" /v "default ui theme" /t REG_DWORD /d 0 /f
:: Dark Gray
reg add "HKCU\software\policies\microsoft\office\16.0\common" /v "default ui theme" /t REG_DWORD /d 3 /f
:: Black
reg add "HKCU\software\policies\microsoft\office\16.0\common" /v "default ui theme" /t REG_DWORD /d 4 /f
:: White
reg add "HKCU\software\policies\microsoft\office\16.0\common" /v "default ui theme" /t REG_DWORD /d 5 /f

PowerShell

# Common: create the key
New-Item -Path 'HKCU:\software\policies\microsoft\office\16.0\common' -Force | Out-Null

# Options (use only one)
# Colorful
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common' -Name 'default ui theme' -PropertyType DWord -Value 0 -Force | Out-Null
# Dark Gray
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common' -Name 'default ui theme' -PropertyType DWord -Value 3 -Force | Out-Null
# Black
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common' -Name 'default ui theme' -PropertyType DWord -Value 4 -Force | Out-Null
# White
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common' -Name 'default ui theme' -PropertyType DWord -Value 5 -Force | Out-Null