The rootstock, Multiflora rose, has taken over. Since you haven’t seen red/yellow Joeseph’s Coat for a while, he’s probably not coming back...you keep the white shrub if you like it.

When you say you thought "it was a goner", do you mean the plant appeared dead, or what? Are the white flowers similar to what Joseph's Coat should look like, only in white? Or, are they smaller and single? If the plant appeared dead and now there is something growing and flowering there, perhaps it may have been budded on R. multiflora and the stock is now suckering. Or, if you have multiflora growing in the area, perhaps birds (or other critters) dropped seeds which have germinated near where the Joseph's Coat grew and are now flowering. R. multiflora looks like this.

If you mean the Joseph's Coat just looked terrible but wasn't dead and it's now flowering as expected, only instead of the proper coloring, the flowers are washed out toward white, you may have had some freeze damage or the weather has influenced the flower pigmentation, which will probably be more normal once the heat arrives and the plant starts growing and flowering normally. Photos of what you're seeing would probably help diagnose the issue.