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<style name="AppTheme" parent="Theme.MaterialComponents.Light.DarkActionBar">
change this to :
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
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// If you're in an activity:
Button11.setBackgroundColor(getResources().getColor(R.color.red));
// OR, if you're not:
Button11.setBackgroundColor(Button11.getContext().getResources().getColor(R.color.red));
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startBtn.getBackground().setColorFilter(Color.BLUE, PorterDuff.Mode.SRC_ATOP);