there might be some exotic species that tend to be more on the white side typically (e.g. s. ehrenbergi or some deepwater?) but i agree with randall that it's more likely a stressed or young sarco that appears as such.
as sarcos grow they will change color and morphology. sometimes this is a function of the envrionment (light, flow, and food) and sometimes it's genetic. for instance, almost all sarcos start out in the common "toadstool" shape when they're young (either sexually propagated or asexually propagated). but as they mature, some species will morph into their adult forms that look very little like their young states, e.g. s. latum or s. roseum.