I have an issue with some files (PSD, AI and PNG) with transparent background that gets a black background when printed and this do not match 100% black color (C:0, M:0, Y:0, K:100). Why does this happen and how can I solve it? The printer house has adjust the rip in the printer but the problem still excist, so something must be done in my files/document. In InDesign there is no sign of any background on the images/files with transparent background, everything looks great. It also seems that this issue only appears when files with transparent background is placed on black background (K:100). The files with transparent background have color profile CMYK, Coated Fogra39.
Thanks in advance and I hope to get a quick reply since my production is about to start!