in Infopath i set the default value of a due date field to "today()". the format however when i load the form shows "Year-Mo-Day" format (however is correct data), and it displays a red box around the field with ""Only Date or Date and Time Allowed". If i just select the right date from the date picker it works fine. Also, i did set the Format of the Date field to be "03-12-2013" format.
This happens when your regional settings on sharepoint server is different from those on client machine in which you edit template in Infopath Designer.
This can happen even if your "client machine" is the same as server machine due to differences in regional settings in operating system (Windows) and settings of sharepoint server.
Infopath Designer and Filler use regional settings from local machine Windows while Sharepoint server uses its own settings.
I think it was discussed before "Date picker show format differently when publish as a web-based form in SharePoint Library" though your situation is probably (because you did not mention any details), "aggravated" because you dealing with Infopath form of type/compatibility Sharepoint List Form in which Infopath form is rigidly locked to underlying sharepoint list.
The solution is to use the "now()" function instead of "today()" function.