There is more a possibilty of various metals used in colored inks than black inks. The challenge is knowing whether a company is using soy based inks in which case any colors would be fine or old fashioned inks of which an over abundance of colors could be a problem. It not an easy yes no answer. So that being said I steer clear of using heavily colored ink on cardboard or newspaper in mulching composting or other-wise. I and many I know still use a lot of cardboard and newspaper so I am and you are still making strides toward reuse and helping to change a problem to a positive. Don't dwell on the few not saved but on the many that are saved. Dang that almost sounds spiritual and so it is. Any use where you can, is still better than the alternative . Mother Earth and I for one Thank You for thinking of us and helping yourself at the same time what a win-win. Congrats and
Happy Growing David

I think this has come up on the Soil Compost and Mulch forum more than once, and most agree that it's a myth. From what I've gathered, lead based inks used to be used, but are now more expensive than soy based inks.

Thanks, I appreciate the help!
Heather