The whole dial is actually a representation of James Cameron's expedition down the Mariana Trench.
Blue at the top gradually turning black on the way down.
Just like how the sea is during a deep dive.
The DEEPSEA in Yellowish Green font represents the sub that he used (same colour, or looks like it)
Moving the DEEPSEA from the top of the dial to the bottom of the dial signifies the expedition (going down the Mariana Trench)
Or I might just be talking cock...