Visual guidance (VG) plays an essential role in directing user attention in virtual reality (VR) and augmented reality (AR) environments. However, traditional approaches rely on explicit visual annotations, which often compromise visual clarity and increase user cognitive load. To address this issue, we propose an unobtrusive VG technique based on color vibration, a phenomenon in which rapidly alternating colors at frequencies above 25 Hz are perceived as a single intermediate color. Our work explores a perceptual state that exists between complete color fusion and visible flicker, where color differences remain detectable without conscious awareness of vibration. Through two experimental studies, we first identified the thresholds separating complete fusion, this intermediate perceptual state, and visible flicker by systematically varying color vibration parameters. Subsequently, we applied color vibrations with derived thresholds to natural image regions and validated their attention-guiding capabilities using eye-tracking measurements. The results demonstrate that controlled color vibration successfully directs user attention while maintaining low cognitive demand, providing an effective method for implementing unobtrusive VG in VR and AR systems.