Hi,

You have used custom CSS on that, that's why it is like this. Could you please mention the color name which you want to set on header?

-Regards.

white

Please help.

Use this custom CSS

.com-content.view-article #sp-header {
    background-image: unset !important;
    background-color: white !important;
}

Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.