Is it possible to have coloured timeline bars, just like Edge Animate?
 How do I view all-white symbols in the Library preview panel? Can't seem to find an option to change the default white background colour.
1) You cannot manually change the layer colors like Edge Animate, no. Though, tweens will take of a blue, violet, or green color depending upon the type of tween.
2) You can change the background color of the MC preview in the Library by changing the overall Stage background color through the properties panel with the document itself selected.
Also, it wouldn't hurt to file a feature request to restore the missing functionality to set the library preview panel background color.