Crassula Gollum help

[Benyellow]

I know this isn't a cactus but any help would be appreciated.
Anyone know what's wrong with this crassula gollum i bought a few months ago? The leaves are supposed to be green and red-tipped but it's yellow in mine. And some leaves have grey spots on top of it.
I use chipped granite and those 'cacti-soil' which contains peat and black soil i think. I water it once a week and gave it a half day of sunlight.