Ancient statues were brightly painted, not white.
Greek and Roman marble statues were originally painted: red lips, blue robes, gilded hair. The colour weathered away over centuries, and the Renaissance took bare marble to be the ideal. Using UV light and pigment analysis, researchers now reconstruct the original colours; the travelling exhibition 'Gods in Color' has shown such replicas since 2003.
Useful: What you perceive as 'classically plain' is often just the residue time left behind.
Source: en.wikipedia.org