As can be seen by the variety of responses here, there are lots of successful hunters; that use camo, those that do not, and those required by law to wear certain colours, or amount of colour.
I have had success with, and without camo over the past 40 years.
The biggest lessons learned from my time in the field is:
1) You may be able to fool their eyes, and maybe their ears, but you absolutely cannot fool their noses! Play the wind and use scent control (it does help)
2) Movement is the biggest attractor for the eye. If you have to move, make it slow and steady.
3) Noise/silence can be important to some species, but to other species, noise can be very beneficial. Ie. when calling elk in, they are noisy animals and expect to hear noises from the "bull" or "cow" that is calling to them such as; footsteps, racking brush, scuffing the ground, kicking stones, rattling antlers, pulling grass, etc. It will depend on your targeted species.
4) If possible, give them something they expect to see, such as decoys like the turkey and waterfowl hunters use. The Montana decoys for elk, deer, moose, etc work very well. If in a setup, set them up upwind or crosswind from where your target animal will be approaching, or have a buddy calling, move the decoy around 50-100 yards back and to the side of you so that the target animal is focused on them as they approach and will offer you a side angled shot at their vitals, within youand your weapons effective range. Works very well!
5) Not every animal will act, or react in the same manner, or play by our known rules of engagement. Be prepared for the unexpected, and adapt to your particular situation as it occurs. We can still be successful when all "common sense" and experience tells us it shouldn't work. Great examples above of animals being so focused on other things, that they miss the obvious right in front of them. We do it all the time, why shouldn't animals?