Don't panic, I have had that a lot with my plants if they aint been watered in a while. The ones in peat loose the most roots when I re-pot but so far nothing has died because of it.
I think it is typical of cacti and most succulents to have most of the root ball not functioning. There always should be some fresh looking whitish, plump roots. In the beginning of the plant's growing season, they may be very short and hidden among the ones that died when the plant went dormant. That's why the most experienced grower make sure that their plants are actually growing before they give them too much water.
I removed a cactus from a pot and planted it in my rock garden, as the base of the plant was off green,
more a brown. I loosened the soil around the roots
and discovered that most roots to be white.
Is this a result of rot or drying out?[/quote]