Answer: Red days are days to be looked at in the future!

The red days are "sold" days; days which have been designed by users and which will be available to be looked at. But as the dates of these sites are still is in the future, these pages are hidden right now.

Not before midnight on the corresponding day the veil does get lifted; the calendar-day changes to green, and the content of this page can be seen by clicking on this date!