Android – What does the percentage indicates next to update rollout in new Manage release page in Playstore

The best and recommended way is to use Qt Style Sheet.

To change the text color and background color of a QLabel, here is what I would do :

QLabel* pLabel = new QLabel;
pLabel->setStyleSheet("QLabel { background-color : red; color : blue; }");

You could also avoid using Qt Style Sheets and change the QPalette colors of your QLabel, but you might get different results on different platforms and/or styles.

As Qt documentation states :

Using a QPalette isn't guaranteed to work for all styles, because style authors are restricted by the different platforms' guidelines and by the native theme engine.

But you could do something like this :

 QPalette palette = ui->pLabel->palette();
 palette.setColor(ui->pLabel->backgroundRole(), Qt::yellow);
 palette.setColor(ui->pLabel->foregroundRole(), Qt::yellow);
 ui->pLabel->setPalette(palette);

But as I said, I strongly suggest not to use the palette and go for Qt Style Sheet.

Update :- Talked to a Googler working with Google Play console team regarding this issue. One misconception I had at the time was that you need to retain an APK if you want to have a staged rollout. I discussed this with him, and he clarified that it is not needed. Even in staged rollout, with no retained APK, Google play will show an install option to users who visit the app's page. Hope this clears doubts for someone facing similar issues.

I was having the same problem and I fixed without clicking "Retain" for previous version and uploaded a new one and then "Start Rolling" button turn into clickable and done!! ^_^