2 yo son with tonic-clonic seizures and blue extremities

My son had a VSD (hole) repair in his heart when he was 1 yo. Post surgery, he had an infection and this led to cardiac arrest for 8 minutes. After arrest, for 4 days he had multitude of seizures and was given phenobarb/dilanten. His MRI showed slight injury in the motor control region of the brain due to duration of arrest. Miraculously, he walks and seem to be normal. However, he does have seizures (4X/yr on avg.)when he has a fever which I think is from any bug a toddler gets at this age. Sometimes the seizure (avg 1min 2X) is initiated first then the fever which lasts about 2-3 days, or it is the reverse. The strange thing is that his extremities and lips turn purple/blue, avg. 30min before the seizure, and he looks uncomfortable, shivers, becomes clingy, but breathing is good. Anyone know why? Should we be concerned? Cardiologists say it is not related to his heart. Sat has not been possible to measured when he is discoloured but after it is good. His is on frissium (clobazam).