If you have knowledge of HTML and CSS it is a very easy task for you to change the colors.
Step 1: Login FTP or Cpanel
Step 2: Go to whmcsdir/templates/hostx/css
There will be a custom color CSS file there “custom-color-scheme.css” you can write your new CSS in this CSS file.
In case you do not find the “custom-color-scheme.css” file, then create a new one and get it included in the head.tpl file. Follow this procedure to include this CSS file in the head.tpl.
Step 1: Go to whmcsdir/templates/hostx/includes/
Step 2: Find the head.tpl file.
Step 3: Create a backup of the file and edit it.
Step 4: Add the following line of code:
<link href="{$WEB_ROOT}/templates/{$template}/css/custom-color-scheme.css" rel="stylesheet">
The code line should be added as mentioned in the screenshot above.
Step 5: Save the file and upload it.
Step 6: Now you can write your custom color css codes in this newly created custom-color-scheme.css file.