【Whiten】 ,  【blanch】 ,  【bleach】 ,  【decolorize】 ,  【etiolate】  can all mean to change from an original color to white or almost to white.

To  【whiten】 is to make white usually by the application or addition of something from without.

To  【blanch】 is to 【whiten】 by the removal or withdrawal of color or by preventing it from developing.

To  【bleach】 is to 【whiten】 or lighten in color, especially by exposure to sun and air or by chemical processes.

【Decolorize】  implies the deprivation of color (as by processes of bleaching or blanching) but does not carry as strong an implication of whitening as do  【bleach】  and  【blanch】 .

【Etiolate】 is a scientific term used in reference chiefly to plants from which sunlight has been excluded with the result that the natural coloring of chlorophyll is not formed.