It should behave like colors and be drawn from the enclosing decorating box's style.
Created attachment 246694 [details] Patch
/Volumes/Data/EWS/WebKit/Source/WebCore/accessibility/ios/WebAccessibilityObjectWrapperIOS.mm:1768:19: error: no member named 'getTextDecorationColors' in 'WebCore::RenderObject' renderer->getTextDecorationColors(decor, underline, overline, linethrough); ~~~~~~~~ ^ 1 error generated.
Created attachment 246755 [details] Patch that works on iOS
Created attachment 246756 [details] Patch that works on iOS
Fixed in r180273.