Oncidium Twinkle Leaves white, cause?

[Goatherder]

I acquired this plant in March. It was a mail order plant and came a little beat up from traveling. I repotted it.

It has grown ok, and now has some flower spikes, so that it seems to me that the plant is happy. But, I am wondering what is going on with the white (almost bleached looking) areas on some of the leaves. This seems to be mostly on the old growth leaves.

Any ideas as to the cause for this?