Map layers: Base solid fill color transparency is not applied if global transparency is set

[wilmaier]

Package
@itwin/map-layers

Describe the bug
The transparency issue only occurs for solid fill color. If a base map layer is selected then the transparency slider is applied in addition to the global transparency.

To Reproduce

1. Open an imodel where map layers can be enabled.
2. Open map layers widget and enable using toggle
3. Click on settings icon and set transparency to 50
4. Select Solid Fill Color in base dropdown
5. Set transparency slider to 20, 40, 60
6. Note that no change is seen in the viewport background fill color transparency

Expected behavior
The solid fill color transparency should behave the same as for any of the base map layers where the transparency is applied in addition to the global transparency.

Screenshots
Global transparency set

Solid Fill Color transparency not set

Solid Fill Color transparency set

[mdastous-bentley]

if you skip step # 3, can you still reproduce?

[wilmaier]

No the issue only appears if the global transparency is > 0

[mdastous-bentley]

@markschlosseratbentley It looks like a rendering issue, what do you think ?

[markschlosseratbentley]

Certainly possible.

1. Is it dataset-specific, or able to be reproduced with any dataset?
2. Can a saved view + dataset be provided which shows the problem?
3. Is there a workflow in display-test-app which can reproduce the problem?