Display::Style is supposed to have a completely resolved color (cf https://github.com/WebKit/WebKit/blob/main/Source/WebCore/display/css/DisplayStyle.h#L47). ShadowData object contains unresolved StyleColor object. Display::Style should not use ShadowData but a custom object containing shadow information and a Color (resolved by definition) instead of a StyleColor (unresolved by definition).
<rdar://problem/103141629>