It does seem ridiculous you cannot update this in the preferences.
I did notice that the ends of the Modify Frame markers are Blue on the Left and Green on the Right. If I collapse the Multi Frame Modify Markers to the end of the animation, as in the last frame of the section of animation you want to include in the within the markers, and drag the left Mark Back to the left, all the tweens are shown in Blue. And likewise pulling it Right they are now shown in Green. Maybe this would help, you would have to be mindful of it every time you choose to edit multiple frames.
Otherwise I would add a Guide layer of Flat alternate colour you can switch on and off when you need to adjust your animation using onion skin tool. Make sure it's set to guide so it never gets published with your animation.
The product team is looking at this feature request on priority. Stay tuned for updates.
- Pattern brushes
- Frame picker
- Layer transparency
- Improved web publishing options
- Merging JSON/JS code
- Support for transparent canvas background
- HiDPI compatible HTML5 canvas output
- Responsive scaling
- Transparent and responsive OAMs
- Author-time bitmap snapping
- Preloader in HTML5 canvas
- HTML5 canvas publish template improvements
- JSAPI support to import and export HTML templates for canvas documents
- Publish canvas assets to root folder
- Center stage
- Other enhancements
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