My work is very mentally intensive and requires concentration. I find normal Workrave break alerts too intrusive - i.e. while I am in the middle of typing or reading the break alert intrudes at a point in my workflow where it not necessarily convenient or helpful to break at that exact moment (such as I am in the middle of writing a paragraph or studying an article that requires my full attention and concentration). 

The annoyance over time builds up to the point where I feel compelled to turn the break alerts off completely which defeats the purpose of using the app.

Then I try the quiet mode which seems to be a solution except that the alerts this time are too unintrusive. While I am working using quiet mode I do not even notice that the moment to take a break has arrived or often passed many minutes before.

What I need is a solution half-way between these two.

My suggestion is that quiet mode should include a simple change to the interface - rather than just change the colour to a static orange, make the background of break timer flash alternate colours e.g. red and white. This would be obtrusive enough to alert the user that a break is due since it would more likely catch the user's eye but not intrusive enough that the user could not continue working for a few seconds or minutes until a more appropriate time to break (such as ending the reading or writing of a paragraph).