I have to do a little research, but my guess is that the colors derive from petroleum-based colorants. Isn't it logical to think that the synthetics in the colors eventually find their way into our water supply after breaking down in landfills?
These colored wraps remind me of the more popular printed paper towels I wrote about last year:
"Can someone give one good reason why we need petroleum-based dyes on paper towels? Talk about waste for no reason! If we are relying on printed paper towels for kitchen beautification, we have larger interior design issues. One national brand’s web site advertises that 'with a whole range of designer prints, cleaning is now stylish.' Whatever."