The article below will take you through how to set a theme color. find the following steps useful.
Click on Admin on the left-pane to reveal the various functions of the admin role.
Click on Manage Landing Page
OR perform a quick search using the ‘search for activity field with relevant search terms
2: Locate ‘Theme Selection’ to select the desired theme by clicking on any of the theme colors listed below.
3: Click on ‘Save and Continue’ to save the current selection