Biosilk Color Therapy Lock & Protect Leave In Treatment (U) 67Ml Hair Conditioner Biosilk Color Therapy Lock & Protect Leave in Treatment, prevents color fading. Biosilk Color Therapy Treatment, silky soft hair. BIOSILK Color Therapy Lock & Protect Leave in Treatment is the ideal treatment that can be applied to colored hair. This treatment does not need to be rinsed away and protects the colored hair from external influences such as UV radiation.