The blackened tissue is frost bite, and it is probably painful. It is definitely stressful and has been associated with reduced fertility. The whitened tissue at the tips is just cold, not quite frostbite. It might be uncomfortable, but to my knowledge it doesn't seem to stress them much, if at all.
If you are in a cold climate and do not provide heat in your coop, you should seriously consider limiting your choices to breeds with low, thick combs that are known for cold hardiness, the next time you get chicks. The low thick combs have much less surface area exposed to the cold and do not tend to suffer frost bite. Or, just be sure none of your roosters have large single combs. Their combs are much bigger than hens' combs, and therefore more susceptible to frost bite. I have 2 barred rock hens which have small single combs. My rooster and all the other hens have pea or rose combs. No frostbite, and I don't provide heat.
I wouldn't say heating is bad, but it might cause some problems. I know it's been debated a lot here. Right now, you have the birds that you have, and would probably be better off providing heat if you can, if you are already seeing frostbite.