You have ordered labels with black as the only print colour. However, your files were created in CMYK. Please set the colour as 100% black (C=0, M=0, Y=0, K=100).
If you have set the four-colour black on your file to make it darker, we would like to point out that in digital printing we also have the option of printing black twice (“double hit”). This way we achieve the best results with black and produce a particularly deep black. Please contact our customer service team to activate the “Double-hit Black” function for you.