If the question is "How to change a button's color?" the answer is probably something like
myButton->setStyleSheet("background-color: red;");
If the question is how to "How to change the button's color WHEN some conditions" the answer could be
[Somewhere inside a method]
if (conditionsMet) {
Q_EMIT(ChangeButtonColor());
}
[somewhere in constructor, most likely]
connect(this, &MyClass::ChangeButtonColor, this, [m_button](){ m_button->setStyleSheet("background-color: red;"); });
This is one way to connect signal/slot to actually change the button's color when some conditions are met. But the condition can be in another class than the one owning the button, the signal can be emitted by another component and not inside a method, and the code that changes the color can be in a method instead of a lambda.
What might be useful would to copy/paste some code to help you more specifically.
EDIT:
@J.Hilk 's solution, tho a bit complicated for a beginner, is much more robust and pro. It depends on how serious your project is and if you have sufficient knowledge in Qt.
