Header is ob blog page grey

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.

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.