It should be and remain a healthy blue-green all the way to the bottom.
Sounds like it may be a problem with the water supply in summer - if branches of most conifers die they will not grow back, but it does not always show up straight away as you can't see them wilting. Did you water it at all in dry weather?
It is also possible that it might have got too wet - root rot would have the same effect.
When you think you have the answer and if you can improve the situation and if the rest of the tree is still green, it is up to you to decide if it is worth keeping, maybe plant a small shrub in front to disguise the damage. Otherwise you have a new planting opprtunity