1. A method of modifying colours of text extracted from an image of a document page to improve visual quality, said document image comprising text and image regions of various colours, the method comprising: (a) dividing the document image into a plurality of connected components, the connected components comprising pixels of similar colour that are closely spatially located, and selecting from said image a plurality of the connected components that represent text; (b) grouping said plurality of text connected components to form a logical structure grouping of said page comprising one or more text blocks wherein each said text block represents a text line or paragraph; (c) forming one or more logically consistent colour sets for each said text block based on the colours of said connected components in said text block, wherein said logically consistent colour sets represent all text of visually similar colour of the corresponding text line or paragraph; and (d) applying colour enhancement to said logically consistent colour sets to enhance visual quality and correct image defects in the document image.