Step 1 :Log in to your Joomla site as the administrator.
Step 2: Go the Templates > Styles under the ‘Extensions’ menu from the admin panel
Step 3: Now switch to the administrator templates list and open the ISIS default template.
Step 4: Once you are inside of the default template, click on the “Advanced” tab from the menu.
Step 5: Now use them in “Nav Bar Color” and “Header Color” fields to change the default color of your Joomla admin dashboard