Yellow spline points have had their heights fixed to a particular value. Raising the ground level will bury the spline point. lowering the ground height will leave the spline point floating in the air.
White spline points have not had their heights fixed so they will move up and down with the ground height.
For track splines (procedural tracks only) a red colour indicates that the junction at that spline point has not been correctly made. It will still work but it will lose its procedural features.
