A robust finding in the Stroop literature is that congruency effects are larger for color words presented mainly in their congruent color than for color words presented mainly in incongruent colors. However, the nature of this item-specific proportion congruent (ISPC) effect is debated, as it might be produced by either a conflict adaptation strategy (e.g., prepare for conflict when the word RED appears) and/or a more general learning mechanism of stimulus-response contingencies (e.g., prepare to respond blue when the word RED appears). Thus far, attempts to directly dissociate the two processes appear to indicate no role for conflict adaptation, at least in situations in which contingency learning is also possible. We re-examined this conclusion in a Stroop task in which contingency learning and item-specific conflict frequency were manipulated partially independently. In addition to a contingency-learning effect emerging from stimuli matched on conflict frequency, a conflict-adaptation effect also emerged on stimuli matched on contingency. The two effects also had different time courses, with the contingency-learning effect emerging early and remaining stable throughout the experiment and the conflict-adaptation effect arising later in the experiment. These results challenge not only the contingency learning account of the ISPC effect, an account which denies the existence of conflict adaptation, but also control accounts that assume that such a mechanism does exist but is not used when contingency learning is also possible.