UMG Retainer Box renders incorrect colors with Color Vision Deficiency enabled

When using a Retainer Box in UMG with Color Vision Deficiency enabled, the content inside the Retainer Box is rendered with incorrect colors compared to the rest of the UI. This bug is present in UE 5.5, 5.6, and Main P4 CL 45195475.

As an observation, applying Set Color Vision Deficiency Type after a delay in the UMG OnInitialized event and setting Render on Phase = true and Phase to 1 in the Retainer Box can result in the correct color being displayed, but this solution only works when the color vision deficiency is applied inside the UMG UI. The repro project demonstrates that when Color Vision Deficiency is applied at Begin Play (before constructing the widget), the Retainer Box displays incorrect colors.

1. Open the provided repro project in UE 5.5 or later.
2. Open the BugRetainerColor level and start Play in Editor.
3. Observe the UMG UI: right half of the screen is displayed inside a Retainer Box.

Expected result: Color Vision Deficiency should apply consistently to the entire UMG UI.
Actual result: Retainer Box renders with incorrect colors compared to the rest of the UI.