Sometimes roots are brown because of the potting medium (as in stained by). Was it in bark? With oncidiums I find I have to feel them more often than not. They could also be dead/dry roots. IF they are dead, then you run into some trouble because oncidiums tend to grow most of their roots, if not all, as they put out a new growth/pseudobulb.\
From looks alone I cannot judge, but they appear to be fine (sometimes they look fine but aren't firm and are actually soggy sponges instead). It appears that you have something in the Encyclia family so if you look up general culture/care for them you'd probably fair pretty well.
Many encyclia are fragrant, so make sure you smell yours at different times of the day to see if it is