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This study aimed to investigate the phytochemical composition of different parts of Radermachera ignea and to evaluate its potential as a natural dye source for cotton and silk with enhanced wash and light fastness. Phytochemical screening of bark, leaves, and flowers was conducted using standard qualitative assays, while dye extraction from fresh and withered flowers was performed using aqueous and ethanol solvents (25–95%). Dyeing experiments incorporated natural and metal mordants, followed by colorimetric evaluation (L*, a*, b* system). Wash fastness was assessed using simulated ultrasonic washing with sodium lauryl sulfate, and light fastness was evaluated under UVC irradiation to accelerate photodegradation. Results revealed that bark extracts were rich in flavonoids and anthraquinones, while leaves showed high levels of saponins and steroids. Flowers contained significant terpenoids and reducing sugars. Statistical analysis (ANOVA and Duncan test) demonstrated significant differences (p < 0.05) in color properties across extraction methods and mordant treatments. Withered flower extracts obtained using 75% ethanol produced superior dyeing performance. Natural mordants such as tea leaves and banana sap enhanced red coloration and improved durability, while metal mordants (copper and iron) significantly increased yellow tones and color stability after washing and UV exposure. In conclusion, R. ignea flowers represent a promising sustainable natural dye source, with optimized extraction and mordanting strategies significantly improving textile color quality and fastness.