ch panel. Taking into account all data points betweeen z$=$0 and z$\sim$2.5 one sees a clear trend of decreasing size with redshift for all three mass bins. However our data suggest milder size evolution for the most massive early-type galaxies between z$=$1.2 and z$=$0.4, corresponding to a 4 Gyr interval of cosmic time.

The depth and high spatial resolution of the ACS images also allow us to probe in detail the [*intrinsic*]{} colour distribution of the galaxies (i.e. the colour distribution within each galaxy). We follow the approach described in @fer05 which, in a nutshell, registers the images in the two bands considered for a given colour, degrades them by the Point Spread Function of the other passband, and perfoms an optimal Voronoi tessellation in order to achieve a S/N per bin around $10$ while preserving spatial resolution. The final binned data is used to fit a linear relation between colour and $\log
(R/R_e)$ from which we determine the slope and the scatter about the best fit (using a biweight estimator). Figure \[fig:clr\] shows the observer-frame V$-$i colour gradient ([*bottom*]{}) and scatter ([*top*]{}) as a function of stellar mass ([*left*]{}) and half-light radius ([*right*]{}). The black dots correspond to binned data in stellar mass, showing the average and RMS value within each bin. Notice the significant trend with increasing stellar mass towards redder cores (i.e. more negative colour gradients) and small scatter. The colour gradient is in most cases nearly flat, and only for the lowest mass bin do we find significantly large gradients. For comparison, we also show as small grey dots a continuation of the original sample from @egds09 towards lower stellar masses. Blue cores (positive colour gradients) dominate in spheroidal galaxies below $10^{10}$. The homogeneous intrinsic colour distribution thereby suggests no significant star formation and a fast rearranging process of the stellar populations if mergers take place during the observed redshift range. Notice this sample only targe