Child GameObjects appear brighter than expected under the following conditions:

The parent Canvas has "Vertex Color Always In Gamma Color Space" enabled.

One of the following applies to a child GameObject:

(a) It has no SuperSampledUI material assigned.

(b) It has a SuperSampledUI material assigned with a custom _Tint value, and the GameObject is disabled before building the world.

In these cases, it appears that a default SuperSampledUI material is assigned to the UI element at runtime, with _Tint = (1, 1, 1, 1). This results in increased brightness compared to the expected color output.

In the Unity Editor, colors appear correctly both in Edit mode and when entering Play mode.

The issue only manifests after building the world.