First we used classical tweens and the animation worked inside of Animate CC. But now with motion tweens we can`t animate the alpha channel because when adding a keyframe we can only choose position, scale, rotation and all, but color is deactivated. What are we doing wrong?
That is correct. To be able to animate the alpha for TextFields and the like, you need to encapsulate them in a MovieClip. Just right click it and select “Convert to MovieClip”. Then you can add an alpha color effect and animate it.