Everything in Heaven is perfect, and there is no SIN there. . It's the bad things we do. It's anything we think, say, or do that does not please God. The Bible says we have all sinned and displease God. Some sinful things we do are lying, stealing, saying mean things, and not obeying our parents.
Sin has to be punished.
There cannot be any sin in Heaven. We need to get rid of our sin so we can be with God in Heaven someday. There is nothing we can do by ourselves to make us good enough to go to Heaven. RED is the color of Blood. God loved us all so much that He sent His Son Jesus to come to our world to take our punishment for us.