Yes, it can be achieved in Muse and we call it as scroll effect.
Below are some tutorials which can help you
- Scroll Effects: Opacity | Adobe Muse CC tutorials
- Muse Scroll Effects to fade/slide in content as you scroll - YouTube
- Scroll effects in Adobe Muse
You can still search for some more tutorials on google by the keywords "Muse opacity scroll effects"
However, be informed that while using scroll effects you won't be able to use the responsive feature of Muse as the workflow is under development.
That's great to know about scroll effects, so thank you very much. Unfortunately it didn't quite address what I'm trying to do.
As seen in the "Portfolio" section of the aforementioned template, clicking on the buttons shows only the items labeled with the corresponding tags (some have multiple tags as well).
My goal is similar, only the selected items receive an increase in opacity and the others merely stay "greyed out".
My apologies for not being more specific about my intentions.
Ok, I got you.
Something like this can be done in Muse with help of Tabbed panel widget.
Here is an example file on which you can do some more research and attain the desired results -Tabbed Panel, Vertical (Composition Widget) by Adobe Muse Team