Line coloring

I would like to know if its possible to change the color of just a part of a line not the whole line´s color just on part. For example if i want to make the middle of an black line white is it possible to make it happen with just one line? If so how?

I dont think its possible to do what you're asking.
You could however just use different line segments and stick them together.
That is how I would do it.