  The use of metal nanostructures for colourization has attracted a great deal
of interest with the recent developments in plasmonics. However, the current
top-down colourization methods based on plasmonic concepts are tedious and time
consuming, and thus unviable for large-scale industrial applications. Here we
show a bottom-up approach where, upon picosecond laser exposure, a full colour
palette independent of viewing angle can be created on noble metals. We show
that colours are related to a single laser processing parameter, the total
accumulated fluence, which makes this process suitable for high throughput
industrial applications. Statistical image analyses of the laser irradiated
surfaces reveal various distributions of nanoparticle sizes which control
colour. Quantitative comparisons between experiments and large-scale
finite-difference time-domain computations, demonstrate that colours are
produced by selective absorption phenomena in heterogeneous nanoclusters.
Plasmonic cluster resonances are thus found to play the key role in colour
formation.
