The left is the playhead, the right is the skimmer. The skimmer can be in two modes, timeline skimmer or clip skimmer. That is toggled with View>Clip Skimming. Clip skimming only skims the single clip touched by the cursor, vs skimming all clip layers at the location.
The yellow color happens if "snap" is on and the playhead or timeline skimmer is at a "snappable" location. Snapping can be toggled by the icon at upper right of the timeline or with View>Snapping.