Hmm. I killed my Sweet Sugar, but maybe I can help yours. Onc. alliance roots can be tan, white, green, sometimes brown-ish, if they are firm and not squishy or woody feeling they are good. Your roots don't look all that great, but with care it should start growing new ones. If you watered once every two weeks in lava rock, that was definitely not enough, at this time of year you are looking at watering every 2 or 3 days in lava rock. Also you want the plant potted firmly in the medium, as too much movement around the roots will scrape them raw and kill them. Basically, clean it up, pick a medium, pot it so that it is stable in the medium, and give good culture. I would get it out of the pot and medium, get new medium, bleach the pot, and soak the plant in some brookn's for about 20 min. rinse well (make sure all the bugs are off it, tweezers help), and pot it up. It will need some good humidity, and tlc for several weeks.
AOS | Oncidium