It's "bloom" and caused by temperature changes (ie, melting, then cooling) if you didn't temper the chocolate when you melted it. It shouldn't affect the taste, though.

You need to temper the chocolate. Easy to do. The white shouldn't affect the taste although sometimes I find that untempered chocolate tastes a little grainy.

I made a batch of peppermint bark with candy canes and Ghiradelli chocolate chips (semi-sweet and bittersweet). A week later, the chocolate has little white lines and/or dots on it and it seemed like it tasted strange. (The latter could maybe have been because I was biased by the appearance?) Anyone know what happened and how to avoid it next time?? Thanks.