When I put a a color hex #ff00ff inside Ai, the hex number stays the same but the color gets darker and less neon. I've checked and the document was created in RGB mode, and I switched to CMYK and still have the same issue.
You can see an example of the correct color versus darker in the screenshot below:
here is #ff00ff properly displayed:
Here's how it renders when I use the same code in illustrator: