Can I edit several animation curves at a time?

Hello. I want to darken a sprite by frame, so I want to create animation clip to decrease SpriteRenderer Color.r,g,b value gradually.

In Animation Curve Window, I can select and display 3 curves. On frame 0, the value of all curve is 1, on last frame, 0.

I want select these 3 keyframes on frame 0 (or last frame) and adjust their tangent at a time, but I can select only one key frame.I want Color.r,g,b have same curve, but I can't edit them at a time.

Can I edit these curves at a time, or, copy a curve and paste to other curve?

Sorry my English is limited. I thank you for reading it through.