[whpalmer4]

Create a task that is in all ways how you want your newly created tasks to be*— background color, duration, effort, etc. Select Project->Set as Default for New Tasks and all tasks you subsequently create for the project will use that as a template. (Note however that if you change your "template" the existing tasks will not update, OmniPlan just takes a snapshot of what your task looked like at the time you issued the command).