[Dual Shade] Adapt shade colors and transparency to match the UX spec.

Bug: 370556579
Bug: 388470180
Test: Manually by opening the quick settings shade and verifying the
 colors appear as expected.
Test: Existing unit tests still pass.
Flag: com.android.systemui.scene_container
Change-Id: I1cf7a2f2aa906c80594bdc5506a655a33c583aa5