Yellow-leafed cultivars usually do not grow as vigorous as their green-leafed counterparts, which affect their use in landscapes. To breed Forsythia cultivars with both yellow leaves and vigorous growth, crosses between F. ‘Courtaneur’ (♀) and Forsythia koreana ‘Suwon Gold’ (♂) were conducted, and 52 F1 hybrid progenies with different leaf colors (green, chartreuse, and yellow) were obtained. The progenies were categorized into three groups [Yellow Group (YG), Chartreuse Group (CG), and Green Group (GG)] based on leaf colors. The growth index (GI) and the number of branches and leaves of YG progenies were significantly lower at 2%, 35%, and 34% of GG progenies. As the leaves changed from green to chartreuse and to yellow, chlorophyll content, leaf thickness, and chlorophyll fluorescence parameters decreased and the chloroplast structures were disintegrated gradually, which influenced the leaf photosynthetic activity and led to weak growth. Compared with yellow-leafed progenies, the leaf chlorophyll content and leaf thickness of chartreuse-leafed progenies were significantly higher at 71% and 9%. The chloroplast structure of stroma lamella of chartreuse-leafed progenies was relatively intact. Carboxylation efficiency (CE), photochemical efficiency of PS II (Fv/Fm), and the number of branches and leaves of GG progenies were significantly higher than YG progenies; however, they have no significant difference with CG progenies. The results were promising for breeding new forsythia cultivars from moderate growth and chartreuse leaves.