This is most likely due to your print speed being set too low or the density being set too high. Please set your print speed to "5" and the density to "4" and print. 

On PC: 

Go to Control Panel > Devices and Printers > Right click on Rollo > Printer Preferences > Settings Tab 

Adjust (lower) Speed / Density and click OK. The exact number depends on the type of label you are using. We recommend starting with 4 and 4. If your print is too light, please increase the density setting number to get a darker print. 

On Mac:

The exact number for the darkness and print speed depends on the type of label you are using. We recommend starting with 4 and 4. If your print is too light, please increase the darkness setting number to get a darker print.