The present invention provides a post-fabrication modification approach for the fabrication of colored and chromic materials and sensors using plasma surface modification to covalently bind the coloring agent to the substrate, thus avoiding leaching of the dye. Advantageously, in said methods, said coloring agent is a dye or pigment linked to a radical sensitive functional group, such as an alkenyl or alkynyl functional group, and is applied to the substrate prior to the gas plasma treatment. The methods envisaged herein are generic in nature, which allow the covalent immobilization of various dyes on different materials. The covalently coated materials after plasma surface modification, particularly the covalently coated chromic materials and sensors, can be used in many different applications, such as protective textile and wound dressing applications.