Warning StatusIcon should use black fill for a11y

[AlanGreene]

Changes

To ensure proper contrast for a11y purposes, the warning status icon should use a black fill for the '!' in the middle. The default is transparent which means that in the light theme the contrast is not sufficient to meet minimum accessibility requirements.

/kind misc

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Release Notes

NONE

[briangleeson]

/lgtm

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[AlanGreene]

/retest