RGB colors can often be “out of range” saturated than real pigments can be, while CMYK color gamut is adopted to a real printing ink colors. In CMYK mode all available colors you have on screen can be printed using offset or jet printers.

RGB mode do not have such an ink color limitation. The only limit is display color range.
JPG files in CMUK mode can be opened in Photoshop. Photoshop can display colors correctly, but some other graphics editors or viewers don’t work with CMYK files and can make a great color distortions in this mode.

Hey, i worked as a designer for about 4 years, and out of experience, if you dont want distortions in color when you print, you always send a CMYK file to the printing guys, you got more real control of what the actual print will look like, that said, you need a calibrated monitor and photoshop and so on…

My camera also makes rgb photos wich is normal, but when you decide to print something, i open the raw file in photoshop wich will have alot of editing options, then i convert to cmyk make any aditional changes that i need and then send to printing companies.

Hope this helps atleast a bit NancyMP.

Ron,
The file format should not affect the colors. However, I would say to avoid JPEGs as they are lossy compression and some information is lost in the compression.

The first rule in printing is that you can never proof on a monitor, no matter how calibrated. Ask for a match proof that is printed on a printed that is calibrated to their printer’s color profile. They should have you sign off on the proof and match it perfectly in the final printed pieces. This little extra step is worth any small additional cost or time in quality control on your image. And if you do need changes you now have an established point of reference for the adjustments in the proof. Also, if the final pieces are not to your expectations I would reject them. Normally, you only have to do that once for them to realize you are not going to accept anything but perfect. At a good printer that should never even be necessary. If you are using the cheaper online printers they work in bulk by ganging up multiple jobs on large single runs and will be much less likely to have precise color consistency. This is one of the reasons I would recommend professionals who are concerned with the quality of their reproductions to use local printers where a relationship can be established and much greater attention to quality and precision is adhered to.

Ron,
The file format should not affect the colors. However, I would say to avoid JPEGs as they are lossy compression and some information is lost in the compression.

The first rule in printing is that you can never proof on a monitor, no matter how calibrated. Ask for a match proof that is printed on a printed that is calibrated to their printer’s color profile. They should have you sign off on the proof and match it perfectly in the final printed pieces. This little extra step is worth any small additional cost or time in quality control on your image. And if you do need changes you now have an established point of reference for the adjustments in the proof. Also, if the final pieces are not to your expectations I would reject them. Normally, you only have to do that once for them to realize you are not going to accept anything but perfect. At a good printer that should never even be necessary. If you are using the cheaper online printers they work in bulk by ganging up multiple jobs on large single runs and will be much less likely to have precise color consistency. This is one of the reasons I would recommend professionals who are concerned with the quality of their reproductions to use local printers where a relationship can be established and much greater attention to quality and precision is adhered to.

Thanks Brian,
Yes, we always get printed proofs and use professional printers. I’m just surprised how wrong the proofs can be much of the time considering that I can take an image file to a local photo photo printing machine and get reasonably good quality colour.
I did find that, when printing a catalogue, their monitor was pretty well calibrated to their prints, so I could do most of the correcting on that. Corrections after the proofs were minor in comparison, (although the proofs were ink-jet facsimiles of the offset from memory).
So what surprised me was how bad the files looked on their monitor before any corrections. (And I had already corrected the image using an X-Rite colourchecker, so that didn’t have anything to do with it.)

Yes, thanks Brian.