Anthurium andraeanum Lind. is an economically important potted and fresh-cut flower species. However, reduced anthocyanin content under shaded cultivation impacts the color of the spathe, which has negative implications for the marketability of A. andraeanum. Thus, the present study evaluates the use of oyster shell supplementation to the cultivation medium for improving anthocyanin content. Appropriate calcium (Ca) can improve the activity of phenylalanine ammonia lyase (PAL), and PAL activity is positively correlated with anthocyanin content; nitrogen (N) and phosphorus (P) nutrients are closely related to anthocyanin synthesis. N and P nutrients and Ca can alleviate the color symptoms of A. andraeanum when anthocyanin content decreases under weak light (under 220 μmol·m−2·s−1). Microdissolution of calcium carbonate, the main component of oyster shell, can provide better exogenous Ca and adsorb slow-release N and P. Selecting appropriate oyster shell fragments will be the key to A. andraeanum experimental cultivation under low light conditions. Using regression models and response surface methodology (RSM), the relationships between oyster shell fragments and anthocyanin content are promulgated. The main findings indicated that the Ca released from 286-mg oyster shell fragments at pH 5.5 significantly increased the activity of PAL in the pedicel under weak light within 8 hours. At pH 5.9, 375-mg oyster shell fragments could significantly adsorb N and P nutrients within 4 to 14 hours. In conclusion, 286 to 375 mg oyster shell fragments at pH 5.5 to 5.9 could stabilize slow-release fertilizer source and significantly increase anthocyanin content in A. andraeanum spathe.