If the date has a grey background it simply means that the fetus has not yet developed to where you'll get a great look at your baby. While any date colored purple will provide a good look at your unborn child, the darker purple color highlights the most recommended timeframe for your 3D/4D ultrasound. The baby's size is often perfect for a good view and his or her facial features are much more defined.

The light purple timeframe prior to the darker purple will present your baby at a time where his or her features may not be as pronounced or as easy to see. People still get great views of their babies during this time and many choose to do two ultrasounds so that they can see the growth in the womb first-hand.

The light purple timeframe after the darker purple is often just as good but as the baby grows larger he or she may not have as much room in the womb to move around. This crowding can sometimes affect the detail of the ultrasound but it's rare when this happens.