split lines sometimes black, sometimes white

i’m using version 2.03 on OSX 10.8.2 and have many tracks i need to split into different sections.
using the clip command to split, sometimes i get a solid black line and sometimes a white line.
what does this mean and will i be able to manipulate the sections properly?

The split line is normally black, but is white when the editing cursor is over the split line.

The only thing you need to be careful of is that if you click close to a split line. this merges the clips (removes the line). If this happens, Edit > Undo Merge.