I was not implying that the colors were altered after they left the Bank of Latvia, but that whoever does the coloration of the coins after the were struck by the Mint and before they were delivered to the Bank committed the error.
To help other collectors with similar cases, I have started to make a small blog about this type of error: http://errorcoin.wordpress.com/latvian-proof-error-coin/ My research still goes on, so I will continue to develop this blog. Enjoy!