What gives Vietnamese Chicken the red tint? A local oriental restaurant used to sell "Vietnamese Chicken", a hot plate dish of big chunks of chicken breast with onion and spices. The distinguishing feature of the dish was a deep red tint of the chicken meat (on the surface; the inside was normal chicken meat color), even stronger than in the photo:


At one point they must have changed their recipe and the chicken is no longer red, just common yellowish typical to any fried chicken:



I can't really notice a difference in taste (maybe because it was a couple months since I had "red" until I bought "Vietnamese Chicken" and it was now yellow) - still, I'm curious what spice (or whatever other means) can give chicken meat this red coloration, and try making this dish myself. 

(there's a bunch of recipes for this dish, but as I want the "red" variant, I'd like to be able to tell the "red" ones apart from the "yellow".)

Can you help me?
My Vietnamese girlfriend uses "hạt điều màu" (annatto). She heats the nuts in oil and then uses the oil without the nuts to fry the meat in.