Login to your WHM In the Menu, point to Settings and then click Branding Settings.
Click the Control Panel tab and then click the Header link. Here, you have 2 options:

Upload a header logo: Select this radio button to upload an image of your choice as the Header Logo and set the background color for the entire Header area. Header Logo: Click the Choose File button to select the image from your computer as your logo. Header Logo Height: Typically, this should be set as the same height as your logo, in pixels. Header Background Color: You may either click the square box and select a color of your choice or mention the Hexadecimal value of any color in the textbox.