I use entity Framework 4.2 and MVC 4
I Got this model/Database structure
UserInformation
UserID(PK)
FirstName
LastNam
Typically, you would use jQuery to insert a new row. Since we don't know what your code looks like, it's hard to show you exactly how this should be done, but you can look at the examples here:
http://ivanz.com/2011/06/16/editing-variable-length-reorderable-collections-in-asp-net-mvc-part-1/
The trick is that you have to name them appropriately so that the model binder will add them to your collection when you click save. Then you have to write code in your post method to walk through the list of colors and add any records that don't exist already.
This is a relatively complex thing, so it's not something that can be easily covered in a single answer here.
Another option is to simply have an action for the add-new button, and this inserts a blank record into the data collection, which on postback will now get 3 records (one of them with null values). When you fill in the values, it will then postback to the main post method and udate the blank record.
This solution has the drawback that if the user adds a new record and doesn't save, the blank record stays in the database.