CMYK colours are for print, and RGB colours are for screens (read my previous post if you want more info about this). Printed colours will always look duller than they do on screen. BUT we do see super bright printed colours all the time on printed materials and artwork, so I always get people asking me how they can achieve this for their brand.
The answer is spot colours. Spot colours are specially mixed (often to match Pantone colour standards – more on this on another post) ink that allow you to print as bright as you want. So you can have your usual CMYK colours PLUS your bright spot colour.
Spot colours can only be printed by using a Lithographic printer, where plates (templates effectively) are made up as a guide for the ink. This can often be quite expensive, so it’s only cost effective if you’ll be printing a lot of the same thing (eg, for packaging).
It’s definitely something worth considering if you’re doing a large run of packaging or printed material and bright colours are integral to your brand.