Yes, invert may help you see the line easier, but it's not going to tell you if there is color or not. And we all know, if there's no color, it's probably an evap/indent. I use the Aviary app to tweak. I usually up the focus, the contrast and the saturation a little. The saturation is key, because it will pull the color out more and make it easier to see. You just have to play around with the settings. If you would like help tweaking, post pics here and I'll try to do some of them for you! (: