Purple

You know how I carried you on eagles wings and brought you to Myself. Now if you obey Me and keep My Covenant you will be My own special treasure from among all the peoples on earth ; for all the earth belongs to Me. And you will be My kingdom of priests, My holy Nation '
Exodus 19 v 5,6.
Special treasure - segulah, from the root word sagol meaning purple, the colour of royalty.

....... for you are a chosen people. You are royal priests, a holy nation, God's very own possession. As a result, you can show others the goodness of God, for He called you out of darkness into His wonderful light.
1 Peter 2 v 9