One way to do what you are looking for is to use the Workbook.ApplyTheme method.

https://learn.microsoft.com/en-us/office/vba/api/excel.workbook.applytheme

This method uses a theme file located in

C:\Program Files\Microsoft Office\root\Document Themes 16

My version of Excel is

Microsoft® Excel® 2021 MSO (Version 2507 Build 16.0.19029.20136) 64-bit

You can generate your own theme file if needs be but the file OfficeTheme.thmx would be a good starting point. You can then ose the colours in this theme to colour your UserForm.