How to install text color of an QLabel?

On the standard form there is an QLabel with the text, would like to make at form loading text color of an the QLabel red, and after a file choice - green. Has tried:

Code:

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QPalette t_palette = ui->lbFileName->palette();
t_palette.setColor(QPalette::Text, Qt::gray);
ui->lbFileName->setPalette(t_palette);

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Color doesn't change. Prompt, please, as it to make.

Use QPalette::WindowText.

Thanks big, all have turned out.