have u tried the mentioned stylesheet?

t->setStyleSheet("background-color: qlineargradient(x1: 0, y1: 0 x2: 0, y2: 1, stop: 0 #00CD00 , stop: 0.2 #0AC92B stop: 1 #00FF33 );");
its not single color, it contains three colors.
to change different color change the hex code in stop: 0 #00CD00

just copy and paste the stylesheet. its a green gradient with three diff green color

Try and give ur feedback

Bala