The body color state is an important determinant of the value of golden severum (Heros efasciatus)—a popular ornamental fish. The use of dietary supplements to improve the color development and health of this species is unexplored. Herein, the effects of marigold extract (MG) and carophyll red (CR) are examined on the growth, body color development, antioxidant properties, and innate immunity in golden severum. Fish were maintained under controlled water quality conditions (pH, temperature, and dissolved oxygen) and fed six experimental diets containing either 0% MG and CR, 1% MG, 2% MG, 5% MG, 0.5% CR, or 2% CR for five weeks. Both MG and CR significantly decreased lipid peroxide levels in hepatic tissues. In contrast, only MG enhanced the activities of reactive oxygen species (ROS)-scavenging enzymes (superoxide dismutase and catalase). Although MG and CR decreased the respiratory burst activity of splenic leukocytes, other innate immune parameters remained unchanged. Additionally, MG and CR stimulated body color development patterns in golden severum that reflect their unique coloring principles. The ROS-scavenging abilities of MG and CR appear to be related to their antioxidant activity. Hence, MG and CR at the optimal levels of 1.0% and 0.5%, respectively, can improve the body color of golden severum and protect against oxidative stress.