I wonder if it might be a magnesium deficiency? My orchids' leaves get a reddish tint like that if I don't add extra Epsom Salts to the spray fertilizer that I use.
You can get Epsom Salts at the drugstore or grocery store for a couple of bucks. Try dissolving a teaspoon or so in a quart of water and watering it with that a couple of times. It absolutely won't hurt, and if the red is Mg deficiency, it will improve dramatically within a week or two!
Also if it works, I'd keep on adding some to your fert at least through the winter. Plants can't photosynthesize without Mg and it is a highly soluble mineral. Most fertilizers have a tiny bit (listed as a "trace mineral" on the label) but in winter when the sun is not so strong, a lot of tropicals need extra.
