J.,
My daughter had several heart problems due to prematurity (born at 26 weeks, weighing less than 2 lbs after 12 weeks w/o amniotic fluid). She had 2 open heart surgeries before she was even 3lbs.
It is a very good thing that your Dr. is doing a complete exam. The majority of the time that babies are refered to see a specialist it is for screening and preventative care. Many times there are no abnormalities (and your prenatal u/s is a good thing to focus on since they are usually very accurate). When there are abnormalities it is best for Dr's to catch them early on.
There is a wide range of things that can cause babies lips to turn blue (both of my babies had blue lips and for completely different reasons). One possibility is that often with very young babies they have a PDA murmur. It is a shunt that is open during pregnancy that is supposed to close when the baby takes their first breath. Often with premature babies, and occassionally with full term babies this shunt does not close. There are a few simple medications that (most of the time) work. In other cases, such as with my daughter the medication does not work and they go in and surgically close the shunt. I was completely amazed that they were able to close my daughter's PDA when she was not yet 3 lbs. It is a surgery that is done commonly, so the outcome is usually very favorable.
There are many, many other options ranging from normal development with a strange benign behavior to the more serious spectrum.
Please do not worry. Write down any questions or concerns you have ~ pedeatric cardiologists are usually really great at answering questions ~ they realize it is a stressful time for Moms. Our most recent visit for the cardiologist at the Children's hospital resulted in an echocardiogram and an EKG ~ both were completely normal (and the Dr actually expected them to be normal). Her Dr ordered the tests to be able to tell me everything was normal and to reassure me... and also to show her other physicians that her lack of weight gain is not being caused by her heart (now we get to move on to other organs).
See what the cardiologist has to say, then go from there :)... and keep enjoying your new little bundle!
I wish you well.
A.