I have a streaking problem with my buttercream, but only sometimes.
Here are some of my issues:

*I live in southern Louisiana where it is *always* very humid.
*Sometimes my crusting buttercream refuses to crust and I can't use my
roller to smooth it.
*I put the cake in the fridge to help it crust and when I smooth it using a
spatula, sometimes the color streak like in the photo below.

How do I prevent this from happening??

Anyone? I'm sure there is a simple answer but I just don't know it!