pptx: Workaround for text colors inheritance before proper color scheme support.
There's a lot of slides where the text is not visible because text color equals the background color. * Ignore text colors set by slideMaster/slideLayout in case the color scheme changed in slideLayout/slide respectively. Always use the color scheme defined by slideLayout when dealing with defaults because there's a better chance the text is going to be visible. FIXME: Update fo:color in styles prepared while processing the p:txStyles (Slide Master Text Styles) element when a color scheme override is detected. BUG:286101