I would definitely go darker .. you will be surprised how quickly the hot Sun will fade paint especially on the coast !! I'm also a SC Coastal resident and deal with this also !! Your home will be lovely and with your amazing taste you will pick the best color !!
I would do a custom color .... when I go to PB I marvel at the color of the ocean. I think at times it is just the color you're looking for. I think the shutters should have a bit more punch of color than the ones you've shown.
Nimbus blue for sure. To give your shutters some depth of color and not a pastel look.
Although your desire to keep everything pale in color is fine, still I think you would probably like the whole effect better if the three colors are not of the sale value. One needs to be a slight accent, and I vote for the Nimbus blue on the shutters.
Glass slipper is really blue I have it in my bedroom and have asked several bloggers about this color and they all agree interior for sure. I am a designer in Atlanta and trust me paint colors are the hardest to get right. Good luck