I created a coastline of the US on a transparent layer atop a blank white background. I'm trying to just select the coastline so that I can start filling in the ocean and then the land masses... but when i attempt to do that, the lines are selected by color goes everywhere, not just where I want. Is it something I did wrong or is Cntrl+Clicking the thumbnail the wrong way to do it?

I'd attach the psd but the uploader won't let me.