Why a thread of blue?

This is a follow up to my last post on parsha shelach...

The fringes (tzitzit) were to have a thread of blue. Why blue? A couple reasons have been given.

Blue was a color of royalty. All Israel is to be a kingdom of priests and a holy nation. Exodus 19:6. How? By keeping God's commands. And the fringes would help remind them of that.

The blue was clearly distinctive from the white. When it was light enough to tell the difference between the blue thread and the white threads, then it was time to say the morning prayers.
When it was dark enough to not be able to distinguish the blue thread from the white threads, then it was time for the evening prayers.