By default, motion trails display as red lines with white keyframes and pink timing beads. You can edit these colors and other display properties using the Channel Box or Attribute Editor.
To edit motion trail properties
All motion trail color attributes display under the heading MotionTrailShape Attributes.
See also Create Editable Motion Trail Options for more information on motion trail properties.
To delete a motion trail
Select the motion trail in the Outliner (it will be named something like motionTrail1Handle) and press Delete.
To hide a motion trail
Select the motion trail in the Outliner (it will be named something like motionTrail1Handle) and press Ctrl + H. To show it again, select it in the Outliner and press Shift + H.