The green arrow means when the computer analyzed the last round it was undersupplied, the red arrow means it was oversupplied. However, if the plans are updated the arrows will stay until you analyze a new round. By default, all of the plans automatically update after each round.
Also, the computer usually recommends you produce a little extra. The default surplus target is 2 (meaning it will recommend you make 2 more than whatever is planned for consumption). You can edit these values in the government building when you view the laws.