I don't know of any way to change the style of particular transactions. However, typically it's most useful to see the cutoff for only the most recent statement, and this is automatically accomplished if you use the reconciliation feature. Once you reconcile your last statement you can visually see the cutoff where the "y" ends and the "c" or "n" begins.
Another related tip regarding reconciliation is on your accounts page, there is a little drop down on the right side that allows you to display more columns. One of them is "Last Reconcile Date", and then you can see directly on your account page which accounts need to be reconciled. This way you can glance at your accounts and know your numbers are "accurate as of [some-date]". If you have a lot of accounts that need to be reconciled each month this helps quickly show you which ones haven't been done yet.