I just took screenshots of an Android green text bubble and the https://www.android.com/get-the-message/ site, and used Photoshop's eyedropper tool to compare colors. They're the exact same shade of green, #48dd8f.

But it's not just you! The green on Google's site looks visually brighter because the entire bubble is on a blue background. On iPhone, the green is normally on a white background.

Now, try setting your iPhone to Dark Mode in Settings, and you'll find that the green bubbles are still #48dd8f green and the text is still #ffffff pure white; it's harder to read on a black background, IMO.