Blue vs Purple
Be very careful when creating blues for print. 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 rendered to CMYK for printing, the colors may shift and lose vividness.
If we feel that your file may turn purple and you are looking for blue, we may ask you to correct the color and this may also delay your job. We want to make sure that you get your desired outcome. Since color is so subjective we may not always catch this issue, so please, when in doubt, follow the below guidelines.
For example, most bright blues in RGB (RGB is displayed on your monitor) 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. Remember, you want to create your files in CMYK, not RGB.
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 minimum of 25% difference in your Cyan and Magenta values.