They do generally change to the same color(s) every year, but some may turn a different color/shade from one year to another. Where I live (in New England), some years the foliage seems to be more vibrant with lots of reds and oranges. Other years, when weather conditions cause it, it can seem as if most of the foliage is yellow. It's more a matter of shades of browns/brown-reds and yellows - not much orange or bright red.
There are a couple of trees in my yard that always turned yellow (Oaks, I think). They'd make the kitchen have a yellow "light" in it each Fall. I just thought that's the color they turned. Then, however, some trees that had been blocking the light were cut down. The following year those trees that had always turned yellow turned to that "deep peach" with hints of red. So now, every Fall, my kitchen has an orange hue. Another example, last Fall (a weird Fall), the same trees across the street from me, which always turn into a major show of flaming red, last Fall turned sort of dark, reddish, brown and then just turned out-and-out brown.
I suppose, in the case of trees like the yellow-now-peach/orange ones; it was a matter of their being more deprived of light all Spring and Summer, If the other trees hadn't been cut down I'd have never known (after years and years) that those particular trees had the potential of turning more orange (and doing so ever since). :/ But, within the variations caused by conditions like weather (or sun), the tree that turns bright orange in Fall turns the same bright orange each year.