Bubble Coral Skeleton changing color

so i think its the skeleton, it's that white layer that covers the bubble but its gone from a pure white to a cream. is this normal?

here's a pic you can kind of tell the cream color, its normally all white

 

bump

 

I've never owned a bubble coral but generally unless the tissue is receding or turning brown and jelly like or if the coral stops opening up I wouldn't worry about it. Corals do all sorts of funky stuff over the course of the day/week/year.
One thing, are you sure it's supposed to be on the sand? I don't know but just checking, I've always seen them attached to rock.

 

I I have a torch that I literally took from a friend of my daughters. It was in real bad shape w/ alot of the skelly showing. When it started to recover the new flesh was pink and began to cover the skelly like you describe.
Hope this helps.

 

It's probably fine, as mentioned, unless something looks physically wrong with it, then it's probably not a big deal. Remember, the coral is growing and changing everyday.