Most likely it’s 2 images places into the same div, one image is black and the other is white, both are positioned absolute, and with an interaction, they hide/show the upper one.
Depending on how simple the logo icon and hamburger menu are, I’d recommend using SVGs. You can set the fill="currentColor" and change the colors dynamically by modifying the font color of the element. Just create an interaction that changes the text color when a specific element is scrolled into (or out of) view and you can make all the nav elements any color you want.
I’ve actually got a good but temp fix. I created the menu icon with divs and kept them white, then I created “While page is scrolling” interaction on filter - invert. (could work with change color) and then use the live preview to note each section’s percentage.
Quick question, how are you finding and noting the percentage of the sections? I’ve always found the offset field a bit confusing as it always seems require the opposite of my expectation.