Mint green , but be super cautious and pick the Fender brand replacement pickguard in light you know to be similar to what you have where you play. Lots of Pistachio colored PGs to choose from, none recommended with this color guitar.
Btw, and with kindest most respectful regards and all that, but no Pearloid.
I was going to say that very thing - tortoise if you cannot decide over any other colour for a pickguard. Although the aged white or parchment as it's being called now might work. This is what all the new Fender Player Series Stratocasters have.
Here is a pick of my Daphne Blue Tele mid project. I had it down to Parchment vs White. On this particular guitar, I would go Parchment on it if it were reliced or worn. Since it is so pristine with a fresh refinish, I find White looks better.