You should send us your files in CMYK mode since it's the mode used for color printing. If you send us a RGB file, there'll be a color shift when it's converted to CMYK and the printed work is going to look different to the one you sent.
The reason this color shift occurs, is because the RGB color scheme has a greater range of colors than CMYK, allowing it to produce more vibrant colors. Printing colors produced in RGB mode will come out darker and duller than they seem on the monitor. However, because of the greater range of colors RGB mode has, files shown in CMYK mode will always show up accurately on screen.
Here are some examples of how the convertion from RGB to CMYK can affect your images.
To get a better representation of how your final print will look, choose CMYK when creating a new file. Keep in mind, however, that an uncalibrated monitor may not match the finished print.
RGB (red, green, blue) is an additive color spectrum that represents the emittance of light, and when all the primary colors are combined, they form white. Computer monitors and other displays, use the emittance of light to create colors, and therefore, use the RGB mode. However, in printing, inks don’t work the same way. Since they don’t emit light. they use another colorspace to create colors. This new colorspace is the CMYK (cyan, magenta, yellow, black). The CMYK colorspace represents absorption of light and when all the primary colors are combined, they form black.
Due to this differences, it is impossible for certain colors on a screen to be printed, since the CMYK colorspace does not include all the colors within the RGB spectrum. However, you can properly display the CMYK colorspace on a screen, since the RGB colorspace covers it completely.
In this page, we'll tell you about a color shift thay may happen with the color blue and why there's a reason not to design for print in RGB. The range of colors that can be reproduced in CMYK mode is considerably smaller than the RGB range of colors reproducible on a standard monitor, so when the file it's converted to CMYK for printing, the colors will shift and lose vividness.
For example, most bright blues in RGB will turn purple when converted to CMYK because they're outside the range of CMYK colors.
Rather than trying to match that same bright blue, here are some blue mixes that you could use instead.
One way to avoid this color shift is not to use colors that show the gamut warning in the color picker since that means that the color is out of the CMYK range and will shift when it prints. If you click the warning icon, Photoshop will choose the closest achievable CMYK color.
Blue and purple are really close in the CMYK spectrum, so if you want to avoid your blue turning into purple always use a low amount of magenta and a high amount of cyan, make sure to leave at minimun of 25% difference in your Cyan and Magenta values.
How to convert to CMYK in Photoshop from RGB
You can also check if the file you're working with is in CMYK or RGB mode in the tab at the top-left corner of the screen.
Here's how you can change your file mode from RGB to CMYK in Photoshop, simply by going to Image > Mode > CMYK color.
How to convert in Microsoft Publisher
In Publisher you can go to File > Info > Commercial Print Settings > Choose Color Model > Process Colors (CMYK)
You can also change the color model in the Colors selection window
How to convert in PowerPoint
You can't. Note that colors will shift if you use PowerPoint, Word, etc. to make your design.