Happy Spring everyone ~

I have some quick questions about my Cannas, any help would be great :

I saved my Canna bulbs in a wooden wine crate lined with plastic and added alittle bit of soil - In March I placed them in a South facing window, and they are all growing - my questions are :

One some of them, it looks like there is a dead black stripe, running through the leaf or sprout and I was wondering what causes this ? Water, light, soil ect . ?

And should I pot them up now ? Or wait until after frost to get them outside ?

Again, any help would be great ~ Tom