Context:

Our house is 1912 craftsman in climate zone 4c. The house is 2×4 balloon framed. The second floor is a finished attic with cathedral ceilings, shed dormers, and knee walls. The roof is 2×4 framed with fiberglass batts. The exterior of the gable ends is stucco applied directly to board sheathing. I’m not sure whether the gable ends are insulated at all, but according to my thermal camera, they’re easily the coldest surfaces in the house during winter. The ductwork to the second floor is woefully insufficient. The 4 bedrooms and 1 bathroom are supplied by two small registers and no cold air returns.

My specific question:

The bedroom in our south-facing gable end is very uncomfortable outside of the shoulder seasons. During summer days, that room is often 8°F warmer than any other room. That room includes two skylights with unobstructed views of the eastern and western sky. Sitting where the sun comes through those windows is unbearably warm during the summer, but it’s one of the few things heating that room during the winter. How would you recommend limiting heat gain through those skylights in summer while preserving it in winter?

More info on the specifics of the skylights: they’re kinda-sorta-not-really triple-pane. Each one has an older single-pane operable skylight and a newer double-pane fixed window a few inches inboard of it.