  We investigated the radial colour gradient and two-dimensional (2D) colour
properties of 22 E+A galaxies with 5.5 < Hdelta equivalent width(EW) < 8.5\AA
and 49 normal early-type galaxies as a control sample at a redshift of <0.2 in
the Second Data Release of the Sloan Digital Sky Survey. We found that a
substantial number of E+A galaxies exhibit positive slopes of radial colour
gradient (bluer gradients toward the centre) which are seldom seen in normal
early-type galaxies. We found irregular 'colour morphologies'-- asymmetrical
and clumpy patterns -- at the centre of g-r and r-i 2D colour maps of E+A
galaxies with positive slopes of colour gradient. Kolomogorov-Smirnov
two-sample tests show that g-r and r-i colour gradient distributions of E+A
galaxies differ from those of early-type galaxies with a more than 99.99 per
cent significance level. We also found a tight correlation between radial
colour gradients and colours, and between radial colour gradients and the
4000-\AA break in the E+A sample; E+A galaxies which exhibit bluer colour or
weaker D4000 tend to have positive slopes of radial colour gradient. We
compared the GISSEL model and E+A observational quantities, Hdelta EW, D4000
and u-g colour, and found that almost all our E+A galaxies are situated along a
single evolutionary track. Therefore, these results are interpreted as E+A
galaxies evolving from Hdelta EW ~ 8 \AA to Hdelta EW ~ 5 \AA, with colour
gradients changing from positive to negative, and with the irregular 2D colour
map becoming smoother, during a time-scale of ~300 Myr. Our results favour the
hypothesis that E+A galaxies are post-starburst galaxies caused by
merger/interaction, having undergone a centralized violent starburst.
