This coin became rosey pink as a result of being overcooked in the annealing oven. Though many simply become a darker grey, some tend to be copper colored. Some become copper colored in spots, some can also become so even on one side, such as this one I won on GC last night. (MS65 by NGC) Nickels are 75% copper, and it is believed that the copper particles can be drawn outward toward the surface. It sometimes even leaves a copper crust or shell, which can flake off or separate in large sections. Some of you may remember this one I posted awhile ago with just the outer shell and no planchet. (MS62 by PCGS)
Yes. Improper alloy means the percentages of the metals are off. Pretty sure this was discussed on a previous post.