A computer system may identify a first and second predefined color that are found in a Cascading Style Sheets (CSS) style sheet for a webpage. The computer system may receive an object to be embedded in the webpage. The computer system may calculate a color similarity score for each of the predefined colors. The computer system may compare the color similarity scores for the predefined color and determine, based on the comparison, which predefined color is the mask color. The computer system may then mask the object using the mask color.