Every changeset in Crucible may contain a number of amended files. If you add all those changes to the review the checkbox is ticked, if you don't have any of those changes the checkbox is clear, but if you have only some of those changes on your reviews the checkbox will be highlighted as you noticed.
This typically happens when you add some file revisions manually to a review, or add full changeset but then decide to delete some of the file revisions from review.
Hope that helps,
Hmm, either I don't understand, or there's a bug, because all I did was create a new review and use Browse Changelists to select the 2 changelists I wanted to include. The 2nd one down was orange as soon as I clicked it.
This is kind of a weird way to show partial or mixed state. Normally it would show a dash through the center instead of a checkmark.