Your image is a static trajectory of an electron. You obviously try to show the route and all places where the electron has been lived a while as a part of some material structure. The three darker areas obviously have something which makes those areas a little more attractive and the electron has been felt the possible landing points in them comfortable a little longer.
Your options to present the speed in the image:
- do not use static image , have an animation
- paint the trajectory with different colors, have a legend what the colors mean
BTW. Think beforehand what to say to the wise guy who tells that he has red something about the possiblity to know the place and the motion state of an electron simultaneously. You can keep his mouth shut by presenting the trajectory in the animation as fuzzy transition and highlighting the whole substructure where the electron lives a while.