Previous research has suggested that numerosity estimation and counting are closely related to distributed and focused attention, respectively (Chong & Evans, WIREs Cognitive Science, 2(6), 634-638, 2011). Given the critical role of color in guiding attention, this study investigated its effects on numerosity processing by manipulating both color variety (single color, medium variety, high variety) and spatial arrangement (clustered, random). Results from the estimation task revealed that high color variety led to a perceptual bias towards larger quantities, regardless of whether colors were clustered or randomly arranged. This implies that distributed attention may engage in a global assessment of color richness, with less emphasis on spatial arrangement. In contrast, the effect of color on counting was influenced by spatial arrangement: performance improved with clustered colors but declined with random color distribution. This indicates that color interacts with spatial information to modulate focused attention during serial numerosity processing. Taken together, our findings provide new insights into the interaction between numerical cognition and attention, highlighting the need for theories and models of numerical cognition to take into account feature variety and contextual factors, such as the spatial arrangement of features. Additionally, in light of the widespread diversity in real-world environments, our findings could inform strategies to enhance behavioral adaptation to varying environmental conditions.