  Detecting colour changes of a gravitational microlensing event induced by the
limb-darkened extended source effect is important to obtain useful information
both about the lens and source star. However, precise measurements of the
colour changes are hampered by blending, which also causes colour changes of
the event. In this paper, we show that although the colour change measured from
the subtracted image by using the recently developed photometric method of the
``difference image analysis'' (DIA) differs from the colour change measured by
using the conventional method based on the extraction of the individual source
stars' point spread functions, the curve of the colour changes (colour curve)
constructed by using the DIA method enables one to obtain the same information
about the lens and source star, but with significantly reduced uncertainties
due to the absence of blending. We investigate the patterns of the DIA colour
curves for both single lens and binary lens events by constructing colour
change maps.
