First you need to know what a sentence fragment is and also what a complete subject and predict is. That should help you.
Answer:
But the rose-colour swiftly faded." I emphasize with this phrase/quote as it symbolises that the warmth of the colour rose was fading away, which shows that something dreadful had occured for this to happen. The verb "swiftly" means quickly showing a quite similarity of someones life ending. Comparing to the rest of the extract this phrase shows how the sky was drained out of its colour. This phrase implies the sky is slowly loosing its happy touch which gives off some sort of hope to the reader.
