Это был случай одного красен. - Sorry, this is nonsense. I can only guess that you meant something like "this chance/case is as good as any". Not even remotely close to being sure though.

Это был случай услуга за услугу. - This also doesn't make much sense.

Please, provide some context.

Anyway, let's see what can be answered.

Красен is a short masculine form of красивый. Красный is just красный, don't think there is any short form to it, at least one that is widely used.

Услуга за услугу - yes, this literally means "a favor for a favor".