ColorReplace

ColorReplace[image, color] finds regions in image whose pixel values are similar to color and replaces them with transparent pixels.

ColorReplace[image, color -> replacement] replaces all pixels with the specified replacement color.

ColorReplace[image, color -> replacement, d] replaces pixels within distance d from color.

Examples

Replace white with transparent:

ColorReplace[img, White]

Replace blue with red:

ColorReplace[img, Blue -> Red]

Please visit the official Wolfram Language Reference for more details.