Should this maybe be on the Breeze product so the VDG has an easier time finding it?

Perhaps, but there seems to be no Breeze/Plasma theme component, so I've put it here under plasmashell/Theme Breeze.

Is there at least a vdg mailing list?

There is a flag in the bug "Visual Design" setting that will CC the VDG mailing list.
Both of you should know that.

This is how it's supposed to look like:

*icon-only task manager
*light theme

Various active tasks. None selected, none are minimized. There's a gray border around active items.
http://i.imgur.com/QpFtN1S.png

Various active tasks. None selected, none are minimized. Cursor hover over one item; transparent blue area w/ blue border.
http://i.imgur.com/DhetFh5.png

Various active tasks. One item is selected. non are minimized. There's a solid blue background over the selected item.
http://i.imgur.com/5y0ZLZ3.png

Various active tasks. One item is selected, one item is minimized. Minimized item is grayed out.
http://i.imgur.com/afRCEmR.png

Various active tasks. One item is selected, one item is minimized, cursor is hovering over the minimized item. The item is still grayed out but there's a transparent blue area selection w/ blue border.
http://i.imgur.com/WqQ3Wg8.png


In the dark theme the gray border would be white.

Oh Kate was minimized all along, I forgot I had Kate running. Anyways, running apps have a gray border. Running apps that are minimized don't. Items that don't have this border but that aren't grayed out are simply "docked" or "pinned" to the task manager. 

Your visual confusion comes from the fact that you're using the dark theme and using the Konsole icon (a dark icon) as examples. If you instead would've used Dolphin as example you would've not noticed this because even when the icon was grayed out because it's blue the grayscale would be lighter.

I'm seriously confused even by your explanation.

> Oh Kate was minimized all along, I forgot I had Kate running

Well if even you, the designer, have a hard time telling these things apart, then perhaps it isn't the ideal solution.

Do note that previously this was easily recognizable by the blue/gray strip at the top of the task item. Depending purely on greying out the icon cannot be a good idea (think of people with not perfect vision) and as it's showing, with most icons you cannot really tell. Especially since we are actually shipping icons that look about the same in their greyed out version.

And as such, it is a regression from the previous version(s).

> Well if even you, the designer, have a hard time telling these things apart, then perhaps it isn't the ideal solution.

I don't. I just forgot I had Kate running. *It Happens*.

> Do note that previously this was easily recognizable by the blue/gray strip at the top of the task item. Depending purely on greying out the icon cannot be a good idea (think of people with not perfect vision) and as it's showing, with most icons you cannot really tell. Especially since we are actually shipping icons that look about the same in their greyed out version.

Well. Then just replace the svg file with the previous one. Or even better, remove *this* theme in 5.5.1(?) and use the previous as I asked in an another bug.

*** Bug 355388 has been marked as a duplicate of this bug. ***

> Or even better, remove *this* theme in 5.5.1(?) and use the previous as I asked in an another bug.

It doesn't have to be necessarily removing the theme, we just need to add a better differentiation between those two states, that should be simple enough. I would suggest also using the frame for minimized tasks, perhaps at 50% opacity + the desaturated icon. Or something better, I'm sure we can come up with some ideas.

Maybe it is not related, or the problem is worse in breeze dark.

http://gdurl.com/MpWP

In this screenshot chrome was running and not minimized. There just is no state indication.
On the other hand, more than one dolphin instance was running and you can see a strange triangle obstructing the icon almost completely (I'm not talking about the green default application icon).

I will try an see if the problem looks different with another theme.

I can now confirm, that the bevior I described dies not happen with the light breeze theme. Should the bug be somehow reopened with more specific information?

I removed that triangle form the theme. If it's loading it it's because of cache or because you have the previous theme in your system.

Created attachment 95552 [details]
Added minimized task state.

In the image:

Dolphin is running but it's not the active window.
Chrome is running and is the active window.
Inkscape is not running.
Konsole is running but it's minimized.
Kate is not running.
System Settings is running but it's minimized.
Spotify is running but it's minimized.
Filezilla is not running.
GIMP is not running.
Ktorrent is running and the cursor is hovering over it (dark theme)/inactive window (light theme).

I think this is great and I think it solves this bug nicely.

As a side note, I think the running-but-inactive rectangle in Breeze Dark is just too much contrasty and stands out quite a bit; neither the active nor minimized stated have such contrasty edge (and the active task should stand out the most). I would suggest to tone the rectangle border to about half opacity in Breeze Dark. It also looks much cluttered on smaller panels when you have lots of windows opened (and not minimized).

Created attachment 95554 [details]
Changed color of active task.

Changed the color of the running but inactive border to the same color as it's in the Breeze Dark color scheme (6a6e72) and the same opacity as the other elements (60%).

Perfect.

It's a ship it from me.

(and please set bug status as resolved-fixed when it's in)

Git commit 93ade11accc59d66d081e0251233c21952beb3ee by Uri Herrera.
Committed on 20/11/2015 at 09:06.
Pushed by uriherrera into branch 'master'.
Related: bug 6, bug 6, bug 72, bug 60

M  +-    --    src/desktoptheme/breeze/widgets/tasks.svgz

http://commits.kde.org/plasma-framework/93ade11accc59d66d081e0251233c21952beb3ee

*** Bug 356004 has been marked as a duplicate of this bug. ***

Hmm... I'm really confused... On Arch Linux with Plasma 5.4 using normal (light) Breeze theme the distinction between minimized, visible, etc. was working without any issues. Today I upgraded to Plasma 5.5 and the distinction is gone - all the icons on the task manager look exactly the same, no matter whether the application is minimized or visible. When I switch to Breeze Dark I can see the frames and backgrounds. When I switch back to Breeze (light), the distinction is gone.

Should this feature (frames, backgrounds, desaturation of icons, ...) be enabled somewhere in the system settings?

Thanks for any help!

Ok, I managed to fix that myself... I deleted whole ~/.cache folder and now I see the frames (;

Well, for me this bug is still present in 5.5. Neither light nor dark theme make minimized apps distinguishable even after clearing the .cache folder.

Never mind, the update to 5.5.1 fixed it for me.