By default, as you read new discussion posts, Canvas will mark them as read (changing the indicators from blue to white) as you scroll down the page. However, you can manually mark each posts back to a read or unread state.
You can tell Canvas not to automatically mark all your posts as read in your Discussion settings.
Note: Once a post's state is manually changed, the post will not change states (become read or unread) until you manually change it again.
A white dot  indicates the reply has been read. A blue dot  indicates a reply is new or unread.
Mark Post as Unread
To change a read post to unread, click the dot next to the post you wish to change.
Mark Post as Read
To change an unread post to read, click the dot next to the post you wish to change.