i am no expert on diseases, but regarding the possibility of "suntan," i've noticed that overexposed plants generally tend to be more red on one side of the leaf than the other, although this applies more to windowsill-grown plants. maybe this oncidium is just prone to purpling...
could it be that the orchid hasn't produced enough roots suited for s/h conditions yet? maybe wait a little..?
hopefully it's not being cooked in the s/h jar... :P
red streaked leaves can indicate a phosphorus deficiency, although it is rare (and i'm sure you're fertilizing)
just some thoughts