Single page with different colored header

and by colour is meant the background colour of the header – as Mike already suspected?

you can look what selectors the background-color of the header is for. and change it via that page-id of your single page.

#top.page-id-46970 .header_color .header_bg {
  background-color: green
}

#top.page-id-46970 .header_color .container_wrap_meta {
  background-color: green
}

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or you can change f.e. the variable that is set by enfold options ( like mike above shows )
these colors are for header:
–enfold-header-color-bg
–enfold-header-color-bg2

where bg is header background-color – and bg2 is header_meta background-color

you can change these settings via filter for one single page only by:

( because the page / post ID goes to the html as class: html_entry_id_12345 we can use that as selector )

function my_avf_dynamic_css_after_vars($output = ''){
  $output .= "\n";
  /*** Override a defined var for a specific page id*/
  $output .= "html.html_entry_id_46970  {\n";
  $output .=    "--enfold-header-color-bg: #aaa;\n";
  $output .=    "--enfold-header-color-bg2: #aaa;\n";
  $output .= "}\n";
  return $output;
}
add_filter( 'avf_dynamic_css_after_vars', 'my_avf_dynamic_css_after_vars', 10, 1 );

replace the color #aaa to your wanted values.

Once the code snippet has been successfully entered, the page/browser caching must be refreshed.

you find the page-id-xyz or postid-xyz on the body tag. You had to adjust the codes above to your id and wanted colors.