There isn't enough contrast to read inactive titlebar text without strain when using the default Breeze color scheme. Other schemes do a much better job at this. I've currently set the color to #7f8c8d which is the color of inactive text, and it looks much better. VDG should consider making the contrast stronger between inactive titlebar text and inactive titlebar, especially since the active titlebar color already marks out the active from inactive windows.

Personally (as a user, not a design expert), I did not notice the dimmed text as problem for me.

I just compared an active and an inactive window:



I noticed there that only the title bar text of the left window is dimmed. The rest of the window has normal black text color. So, one could argue that for consistency reasons either all of the window's text should be dimmed or none at all (readability).

There is a KWin effect called Dim Inactive that allows the dimming of the entire window for all inactive windows. But barring that, I think there is a better argument for keeping the text color of the rest of the window the same as the active window, and dimming only the titlebar text, since most people like to look at the contents of inactive windows, e.g., if you are reading/comparing two documents side-by-side.

I just tried setting the inactive titlebar text dark (same as window text) but I must say I prefer it lighter and having that extra glanceable information as to which windows are inactive.