I understand your feeling and concern towards your baby.
Turning of your baby's finger blue is expected in this condition this happens because there is lack of gaseous exchange so it happens that way. The pure bold which is pumped through left ventricle is passed to right due to the defect hence there won't enough blood pumped for.perfusion. This type of condition is called VENTRICULAR SEPTAL DEFECT. This needs surgical intervention or it may regress itself as time progresses. But any way need to consult a paediatric cardiologist.