White then dark menu font on scroll

First read this please : did you fill in the enfold options on transparency header? or how did you set up your white font on transparency header?
Dashboard – Enfold Child – Header : “Transparency Options” – there is that setting for : “Transparency Menu Color”

The default way would be to set the font color options on General Styling : Logo Area Background Colors – and for transparency see above.
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Have you set a shrinking header? then you can do it page dependent – by using that additional Class on #header : header-scrolled

#top.page-id-123 .header_color.header-scrolled .main_menu ul:first-child > li > a {
	color: red
}