I have heard of a blue spruce but if you have ever seen a purple evergreen be concerned. No this is not some winter color or a change from new growth. Usually that means it has a pest attacking it or a disease it is struggling with. Look for webbing or shake an affected area over white paper and see if any little bugs fall on to the paper. If so, you most likely have mites. Spider mites are a spider like insect (about 0.04 inches or less in size) that suck the juice out of the needles and stems of evergreens. They can also attack other deciduous plants and can be both cold season or hot season varieties. Find a licensed chemical applicator to help further determine what is wrong and help find the appropriate treatment.