A fixed mark can respond to the section beneath it. The useful question is not whether the idea sounds persuasive. It is whether it helps someone understand the work, make a decision, or complete a task with less friction.
What is happening
Scroll position alone cannot describe a page with alternating light and dark surfaces. The element needs information about what occupies its screen position.
This tends to become visible at the boundary between the organization and the person encountering it for the first time. Internal familiarity hides effort that remains obvious to a customer, reader, applicant, or collaborator.
A practical response
Use section theme markers with intersection or point sampling, then animate between approved logo states without recoloring the artwork itself.
The aim is a smaller, clearer system: one source for the record, one visible hierarchy, and one next action that behaves as expected. That approach improves the immediate page and makes later application or database work easier to add without rebuilding the public surface.