Taking all the Severitus in mind, this is the best description of Harry's new looks I have read. I also think the way you wrote Severus' reaction the most credible. This man has been alone too long, his love long dead, so of course he would embrace a son, albeit while hesitant of how good a father he would make. From canon, we also know how Severus, once he knew the truth, would move heaven and earth to ensure his son had the very best of guidance and support. After all, he devoted a lifetime of faithfulness to just one woman. I think he would do the same for Harry.
Very, very well done and a beautifully romantic father-son tale. Your writing was swift-paced, flowing with imagery and exciting to boot. Lastly, your reasoning was handled delicately, such as when Severus tries to explain his theory regarding his survival. None of it came across as the last scene of an Agatha Christie; it was part and parcel of a lovely script, a gentle unraveling for the reader's enjoyment.