colour print out problem

I have created a series of label designs for a client that consist of a different colour vignette on each label but the type is always in dark grey. Each file / design has been created in one layer (due to my lack of expertise in using different ones). The problem is when i send the files -saved as PDF- to my client, and they try printing them on their own printer, the colours are not printing consistently the same and the grey type is a different shade on various designs. Any ideas what is going wrong?