Problem converting color from RGB to CMYK for print

I designed a poster in CorelDraw X5 for printing purposes. I was told by the Printshop guy to use colors only in CMYK. For the most part I did, I don't know why I missed it but I used one color in RGB. I liked this color so much that I've used it at many places. So, current situation is that some colors are in RGB and some are in CMYK. So, I want to convert all RGB to CMYK and thought the problem would be solved. But now I'm actually facing a lot of trouble. The colors are not at all same. I hate the colors that it is showing me.

This is the color I used in RGB:

When I changed the "Model" to CMYK, the color it shows is really different. As you can see in the picture below, it's too dull:

The RGB values of both colors are not the same. What can I do to get the same color in CMYK? I did a little bit of reading here and there. They say, that you can't get same. In that case, what is the closest color that I can get?

Answer

The range of colors that can be reproduced in any CMYK-only color (known in the trade as "Process Color") printing method is considerably smaller than the sRGB range of colors reproducible on a standard monitor. Here is an excellent video that demonstrates this visually using 3D color models.

It happens that one of the ranges of RGB color that can't be reproduced at all is in the relatively "pure" and saturated blues, and you've run into a problem that confronts many a beginning or untrained designer: "everybody's favorite color is blue," but blue doesn't print. This is not the only difficult range. Huge chunks of green and yellow-green, and all the bright reds and oranges just don't appear in CMYK at all. (There are ways to get many of these colors into print, but you have to go beyond just CMY and K into special inks to get there.)

I'm not familiar with Corel, so I don't know if it has a "gamut warning" feature similar to what you'd find in Photoshop or Illustrator to let you know that you're picking colors that are outside the range of CMYK "process colors". What I can tell you is that in this case Corel is trying to give you the closest achievable CMYK blue to the one you picked in RGB. Unfortunately, as you've discovered, it's not very close.

The other thing that may help is to make sure that your CMYK color profile is not set to the usual default of SWOP v2. Not only is this very out of date, it doesn't accurately reflect what is really achievable on modern presses. The best CMYK color space for most purposes these days is Coated GRACol 2006, which is also an ISO standard. If you can change your CMYK color profile to GRACol or FOGRA39 you'll find you have considerably better choices in the blue range. They're still nowhere near the full RGB gamut, but a definite advance on SWOP.