Postman enables you to adapt Postman to your visual preferences in two ways. You can set the theme manually or sync it with the operating system’s appearance settings. Themes auto-sync by default.
If the Workspace Admin customizes the workspace theme colors, this overrides the colors in the application theme you set. Your application theme colors are restored when you leave the workspace.
To apply a theme across the Postman app, click 
Settings in the header and then click App settings. Click Themes.
You can select a single theme to be applied in light or dark mode at all times.
You can also switch the themes based on your system settings, and have a different theme for day and night, respectively.
Not all themes have a light/dark counterpart.