Depends on where you are standing or sitting. I truly believe from 25 years of experience, that clothing that breaks up your outline does help. Even if you are sitting still with the right wind a deer can still pick you out from a good distance if you have little background cover. No its not absolutely neccessary but I firmly believe it gives you an edge in many situations. When I first started bowhunting i wore a olive drab flight suit my dad had given me. The first couple of years I had alot of deer stare me down and get nervous after they caught a glimpse of me up in a tree.
I hadnt moved a muscle and the wind was usually in my favor so I figured the solid blob must have them spooked. I went to an army surplus store and bought my first set of camo. I took some iron on patches and added some lighter tones to the clothing and hit the woods again. There was a night and day difference in the amount of deer I saw and the amount of deer that DIDNT see me.
Camo doesnt have to be store bought and look like a log or leaf type.
Any pattern with large blotches of various tones will work. And plaid IS camoflauge.