It looks like there is a minor color fill bug when setting
EncEnvironmentSettings.displaySettings.marinerSettings.twoDepthShades = false
This should enable the four-color mode, which in particular should show a different color for areas below the shallow depth vs above it. However, I only get three shades and am missing the critical safe/shallow coloration.
The following images are taken from a viewpoint in the Boston harbor area, at 42.34, -70.99.
The first image is from a custom QML app:

The second image is from NOAA ENCOnline.

In the second image, the area between Safe and Shallow is colored differently from the area inside the Shallow contour.
The NOAA map is rendered using ArcGIS, so this points toward a coloration bug in the SDK itself. I don't have any experience with the other SDKs so can't verify if this behavior exists across all SDKs or is only in the Qt/QML one.