Oncidiums and the Alliance alike are heavy drinkers and yet they like to dry out fast. Thing is the lava rock in your area will make it dry out
too fast. I suggest a repot in a small bark mix or coco husk. Lava rock doesn't do well in this area unless you're in a green house with high humidity. The root coloration sounds fine. The white is normal. This color is from the roots being in the pot and not photosynthesis from the sun. Still okay. The wrinkling on the pseudobulbs is from lack of water. Depending on how dry your area is you can water anywhere from 3-5 days, with misting daily. I mist mine daily and water every 5 days. (mist only the base of the plant. )
Oncidiums must have strong ample airflow!!! The leaves on these can get a fungus if inadequate airflow is given. Make sure that you give a nice flow of air where the leaves have a gentle movement to them. This will reduce the chance of spotting on the leaves.
I hope this helps.