If you want a different color popup (now that the default is dark gray which makes the blue linked text illegible) the solution appears to be to change the color of cloud-popup-relative.png. But, it turns out that that file is cached by the browser. Clearing the site cache has no effect on it. So, if you're theming the popup, your users will have different experiences depending on which version of that file is in their browser's cache. Also, if a user visits one Drupal site that uses a gray version of that graphic and then visits another site that uses a white version, would the same png file be used for both sites?
Is there anyway to prevent that png from caching for more than a minute?
I don't know if this request should be broadened to include other resources. I've noticed that some other modules have addressed browser caching issues so I assume it's possible.
If the official response is to code something in PHP or Javascript, could someone please write up a detailed process for those of us who can't distinguish PHP from Sanskrit? Saying "Just theme it using Drupal.theme.openlayersPopup(feature)" causes some of us to look like a deer in headlights. It's not that we're not willing - it's just comparable to asking my teenage son to build an Atlas rocket. The willingness is there - just not the know-how. Thanks.