Grapheme-color synesthetes experience colors when viewing objectively achromatic alphanumeric characters. One major hypothesis states that the color sensation emerges from co-activation of color-selective neurons during sensory processing. In this pre-registered study (https://osf.io/xhd5y), we examine the concurrent hypothesis that color-inducing graphemes are highly salient shapes for synesthetes, which scale up the neural gain during visual processing and increase the probability for a later irregular shape and color integration. Synesthetes and matched controls performed a grapheme detection task while chromatic pattern masks were flashed into the dominant eye. This technique renders target images invisible for an elongated time contingent on their saliency. We predicted a faster break from suppression for color-inducing compared to non-color-inducing graphemes in synesthetes. Because chromatic masks suppress colored targets more than uncolored ones, the opposite pattern of slower responses for color-inducing graphemes should occur from color co-activation. The results showed overall higher reaction times in synesthetes compared to controls, and no reaction time difference between color-inducing and non-color-inducing graphemes overall. The data suggests that both co-activation and saliency do not cause color experiences in synesthesia.