YAY!!!!I can't believe it, I found the yarn I need!Twenty + years ago Red Heart called it Powder Blue, now they called Light Blue and the color matches perfectly.
If I couldn't find the yarn I was going to work it like you suggested. I would make the sky look like it was a storm coming. I would blend it in have the stormy sky behind the masts of the ship.
You may know this, but I'll say it anyway in case it helps someone: look at the two yarns side-by-side under daylight. Not a "daylight" light inside, but actual sunlight.
A good way to check is to take a strand of each yarn, make a few wraps around your hand. If you can't tell the difference in daylight, they should be good to use together.
