Zebra Browser Print SDK - Setting Darkness?

I am using Zebra Browser print with a web application that prints badges for events.

So far everything is working properly, but i am finding that the darkness of the direct printing of the badges could be much better. I am using a Zebra GK420D printer.

Is there any way to set the darkness of the badge? I am using both PC/Mac, i can set the darkness via the driver on the PC, but not on the mac, but for our end user, it would be a little tough to have them install drivers etc... on every machine and go in there and configure the printer settings. I would love to just have it set in the printer input, or via the SDK somehow, and keep the simplicity of the browser print application and how it's fairly plug and play.

Thanks!