What does a green vs. orange/brown target icon mean on airports?

On the World Map, what does a green or an orange/brown icon on the airports/airfields mean?

I thought, at first, it was places I’d landed vs. not landed, but that does not seem to be the case.

Does anyone actually know or know where this change was documented?

If you look at the map legend, it shows the green ones have “approach Procedure and radar minimums”, while the brown ones have “no published instrument procedures”.
Actual U.S. Sectional charts are slightly different, but the meaning of all symbols are included on the charts.
Take a look at page nine of the linked document.