I perfectly know that RGB is for displays and that i always will have problems if i try to print a screen.
IMO you knowledge is not perfect. Displays are not the only RGB devices. And there are many RGB color spaces. There are computer application that color manage imges and applications the do not have color management. There are image files that have embedded color profiles and image files the do not have embedded color profiles. Ther are Image files thet are not saved with rgb colors. So you are in an environment the you need to educate yourself some to know what is going on. You will have problem printing more than just sceens.
What do you mean they are terrible exactly? Is the problem that you are trying to print really bright colours and are disappointed with the dull print result? If so, that's normal. Few printers have special bright inks like that.
Thanks for the answer JJMack. I never said that displays are the only RGB device. But yes, probably i have many knowloge gaps in color management techniques. I am a programmer. So thank you for the puntualization about my skills.
Sorry for the bad description of the problem. But you centered the question. Is totally not bright.
Perhaps exists some conventional tecniques to convert colors, prepare the image or set the color management to minimize the problem?
And if is a matter of printer, can you suggest some kind of printers i should look for?
Sorry for my bad english, I've done my best!
The problem is simple - light reflected through coloured ink on paper will never be as bright as light emitted from a screen. So you will not get those very saturated screen colors in print.
You can predict what will show if you are using a color managed workflow where Photoshop is managing the color for printing and you are using the correct color profile for your printer and paper combination, and you have a correctly set up and profiled display.
If so, go to menu View > Proof Set up and select the profile for your printer and paper.
Then check View>Proof colors
You will immediately see the colors dull as only the printable colors will be used. How the colours that are unprintable are mapped to printable colors depends on the rendering intent that you choose.
Proof using my profile for the Epson as shown above
You can also switch on the gamut warning (View Gamut Warning )and it will show the unprintable colours as a grey overlay.
If you are only dealing with 16 colours you can choose to just allow the color management conversion to replace them with printable colours (as shown by the soft proof) or you could change the colours in the document to printable colours manually.
Dave your answer is extremely useful! Thanks a lot for the clear and detailed explanation.
Thanks also to other people who gave me an answer!