What's up with that little light that changes colors by the big door in Anor Londo?

[Aetrion]

I noticed something while I was playing in the Anor Londo area right before you fight Aldritch. Outside the big door you open with the lever inside of the keep there is a small mote of light on the ground to the right. It's just sitting there, not doing anything. However, it seems to change colors. It started out red the first time I noticed it, then was green, yellow, blue and purple the next four times I went into that area.

I took a screenshot of it so you can see what I mean:

https://steamcommunity.com/sharedfiles/filedetails/?id=683403069

Has anyone else noticed this? Does anyone know what this is about? I mean it could be nothing, but it seems really odd for this light to just hang out there and change colors like that. Is there maybe some kind of secret tied to the color changes? I'm just speculating here, but I haven't seen anything else like this in the game anywhere.

I'm on NG+ in that screenshot.

[Argon]

Looks like a Prism Stone, those are items that can be dropped by players. Prism Stones can be used as decoration for fight clubs, and can be dropped off cliffs to see if the drop is survivable. They can be bought infinitely from the handmaiden.

[Wandering Flare]

It's Anri's prism stone, appears there near the end of her quest line, if you went for the light ending and killed the pilgrim/didn't spawn Yuria at all. But that's as far as I can assume, not a 100% info.

[Aetrion]

I did kill the Pilgrim in the chapel, but Anri hasn't shown up anywhere since. I guess this does explain what the light is though.

[Gyve]

Originally posted by Mr. Scratch:

It's Anri's prism stone, appears there near the end of her quest line, if you went for the light ending and killed the pilgrim/didn't spawn Yuria at all. But that's as far as I can assume, not a 100% info.

can confirm, it's there because of anri's quest.

[Wandering Flare]

Originally posted by Aetrion:

I did kill the Pilgrim in the chapel, but Anri hasn't shown up anywhere since. I guess this does explain what the light is though.

So, if you did, Anri shows she made it to Aldrich, and somewhere near his fog gate will be her sign asking for help.