Apple Color 1.0 - Manual (Page 291)

Chapter 14 Keyframing 291
By default, all new keyframes that you create are smooth, although you can change a
keyframe’s interpolation at any time. Changing a keyframe’s interpolation only affects
the way values are animated between it and the next keyframe to the right.
To change a keyframe’s interpolation:
1 Move the playhead to the keyframe you want to change.
2 Choose Timeline > Change Keyframe (Control-0).