[At some point, whether it's during the Flower Festival or after it, Alice takes the time to present one of the many white flowers to Shiro - a garden rose to be precise. She admits as she does so with some awkward sheepishness:]

Allura reminded me... not that I wouldn't without prompting! If I remembered! I just...

[Aha, well. She's just no good at this, any of it. It's not for the first time she feels somewhat sorry about that.]

They say they change color in time.