I wouldnt print this "as is" on a dark heather unless they insist. I would encourage them to change the navy text to white for sure. As for the fading shapes, I would probably suggest using two blues and using a combination of halftones in the base and mixing the blues to imply the sort of fading to dark effect. The darkest shape would end up just being the darker blue with no base, then for each brighter shade use some percentage of white and one or both blues. Front lightest blue would be solid base, next might be 65, then 30, etc.