If labels sent to print from Shiptheory are coming through as faded, opposed to creating labels via a carriers interface, you may need to adjust your printer's settings.
As some carriers (such as DPD) send through the print quality settings.  Shiptheory uses your printer's default settings.

Thermal printers work slightly different to traditional laser and inkject printers when it comes to changing quality settings, as they are entirely heat driven. Thus you need to increase the heat of the print in the printer settings.

First, find the printer you wish to change the quality of:

Select printing Preferences

You should see a 'print head temperature' setting, where you can change the heat of your print head per print.  This is the equivalent of 'quality' however, you will not want to make it to hot, else the label will end up too dark.

You can also use the 'double heat' option if available, which will double your heat settings, however this could be too hot and again create the labels too dark

You can also modify borders, offsets and orientation of your default print setup for that printer if you need, however a more indepth look at this can be found here