We always print using CMYK.
If you provide us with an RGB file for printing, we will automatically convert it to CMYK before printing. This conversion process can cause the colours in your document to appear differently on paper than they do on screen, as some RGB colours cannot be reproduced accurately using CMYK inks.
To avoid potential colour issues, we recommend designing and saving your documents using the CMYK colour model from the outset. This will help to ensure that the colours you see on your screen are as close as possible to the colours that will be printed on paper.