Why do tetralogy of fallot babies go blue after being born?

Babies with ToF often go blue after being born because their heart rate accelerates making it more difficult for their heart to pump through the stenosis in pulmonary valve (valve to the lungs) and also because they have a large VSD (ventricular septal defect) (a whole between the bottom chambers of the heart) causing oxygenated and deoxygenated blood to mix. Deoxygenated blood has a bluish tinge!