Working with Pantones (PMS)
Unfortunately Pantone colours can be a real pain to work with but they do provide the most consistency when printed. What you see in the Pantone books is what should come out when printed.
Difference between CMYK & Pantone
CMYK – This is made up of 4 separate colours: Cyan, Magenta, Yellow & Black. They are printed one at a time over top of one another to create a range of colours. This is also known as full-colour or process printing.
Pantone – Each colour is made up of one solid ink which is created by the printer using a specific formula. The formula is the same every time so it provides the most consistency when printing. These colours are also known as PMS (Pantone Matching System).
Problems when using Pantones
There are a few problems when working with Pantone colours.
One problem lies with the number of actual swatches in the Illustrator swatch library. This can be confusing as the libraries contain various options for the same Pantone number (e.g. 1505 C, 1505 U, 1505 PC, 1505 UP).
Another problem being that they don’t display correctly when viewing them on screen. Some colours look completely off; sometimes very muddy/dull or significantly darker or lighter than in the Pantone books.
One other problem is that not all Pantone colours convert well when switched over to CMYK. There can be a major colour shift due to the fact that CMYK can’t reproduce some of the brighter or highly saturated colours.
Solving the problems
Problem – Multiple colour swatches with the same number. Note: You can view the various swatch libraries in Illustrator by going to Window > Swatches and then selecting the dropdown at the top right of the Swatches window Open Swatch Library > Color Books > PANTONE xxxx.
Solution – When printing with Pantones, use the PANTONE solid coated and PANTONE solid uncoated libraries depending on the type of stock being printed on. Note: Coated and Uncoated colours (e.g. 1505 C and 1505 U) are actually the exact same ink when printed but the swatches may display differently on screen when View > Overprint Preview is selected so you’ll have a closer visualization of what the final printed piece will look like.
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Problem – The colours you chose from the Pantone book doesn’t display right on screen in Illustrator.
Solution – Although the colours will never display 100% accurate on screen vs. print there is a way to get a closer match. First off, it’s a good idea to have your screen calibrated. Then select View > Overprint Preview. This should do the trick. You can also select View > Proof Colors to see if that helps any further. On a side note, when you save out a file as an EPS be sure to have Overprints set to Preserve if you’ve used them.
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Problem – Converting from Pantone to CMYK causes a shift in colour (sometimes a huge shift).
Solution – For some Pantone colours there is no solution. That is due to the fact that CMYK simply can’t reproduce some of the brighter or highly saturated colours. They just aren’t in the range of colour that CMYK is capable of. That being said, it is best to start off the colour selection process with the Pantone Color Bridge book to see how a Pantone colour will convert to CMYK. If the client knows they will need to reproduce the colour in CMYK then it’s best to choose a Pantone that has a close conversion.
Now comes the process of actually converting the colours over in Illustrator. Some people might be tempted to simply select Edit > Edit Colors > Convert to CMYK (which is equivalent to clicking the 
in the Color window just below the % box). The problem with that is the converted CMYK numbers are not the most accurate possible numbers. Pantone (the company) has released new CMYK formulas which are closer conversions from Pantone to CMYK. To get these new colour formulas select from Illustrators swatch libraries within the Swatches window Open Swatch Library > Color Books > PANTONE color bridge CMYK PC (or) PANTONE color bridge CMYK UP. The swatches ending in PC are for coated stock and the swatches ending in UP are for uncoated stock. Unlike the solid Pantones, the PC and UP versions of a colour number (e.g. 1505 PC and 1505 UP) are actually different. This is due to the fact that the CMYK formulas are different to compensate for coated and uncoated stocks so be sure to select the correct one depending on the stock you will be printing on.
If you have selected a solid pantone swatch (e.g. 1505 C) and then color bridge swatch (e.g. 1505 PC) you’ll notice in your Swatches window that there are 2 different swatches, 
and 
. The one with the dot in the bottom right indicates that it is a solid Pantone colour and the one without the dot indicates that it is a process (CMYK) colour.
Overall Notes
– These instructions are all in reference to Illustrator. Photoshop is a whole different beast.
– Colours on screen will never be the exact same as the final printed piece.
– The Pantone swatch books are your best bet at choosing an exact colour but only if they will be printed as Pantones (not CMYK).
– Some Pantones don’t convert well to CMYK so be cautious of this when choosing a Pantone.
– Use the Pantone Color Bridge book to see how a Pantone colour will convert to CMYK.
If you would like an Illustrator EPS file to test things out you can download it here.