Spot colours are usually from a Pantone Book. These books are available to buy, and contain all the swatches for the coated and uncoated inks that are available in the Pantone range.
You need coated and uncoated swatches because different papers are treated differently. Newspaper is uncoated, where glossy magazines etc. would be coated.
Swatches are little samples of colour that show how the colour will look when printed with coated or uncoated so that you can match that same colour with conistency.
When you add a spot colour to you print job, by applying the swatch to an object, text or graphic in the document it becomes viewable in the Separations Panel (Window>Output>Separations). If you turn off all the Plates CMYK (we'll get to that in a minute), then you will only have that spot colour viewable in the document. This is just a preview of what will be printed onto a plate.
A plate is a metal sheet that is coated with Emulsions, in short, the image is burned on with a laser in a Computer to Plate (CTP) device, waste emulsion is washed off, the plate is gummed (it's a paste the prolongs the life of the plate), and it's then mounted on the press.
Most printing presses have 4 drums, for Cyan, Magenta, Yellow and Black. I don't know how long ago it is since 5 colour presses were in use (that would be CMYK + 1 spot colour all done on the one machine). But in some places they won't have 5 colour press, so they would apply the CMYK to the print job then move the print job to another machine to apply the spot colour. This usually involved heft charges, for machine time and setup costs.
But most modern printers have 5 colour presses, 6 colour, 10 colour etc. presses. So all the extra costs are the CMYK plates, and the Spot Plates and the little bit of extra time to mount the Plates.
Now 10 colour presses wouldn't print CMYK + 6 spot colours – well it could, but it could also mount 2 sets of CMYK plates and then 2 additional Spot Colours.Or any combo they want.
So to answer you question, Spot Colours are specially mixed ink to ensure colour accuracy for specific things, like for example Coca Cola's red colour, it might not be a Pantone colour but it would be classed in some cases as a Spot colour, a specificially mixed ink for that specific Brand.
What you've got here is the opportunity to add a Spot colour to your Newspaper for free of charge. Which isn't surprising, as it should be relatively cheap, and if the company is trying to promote or generate interest in printing 5 colour jobs then offering a free Spot Plate with every print job would be a sure fire way of doing it.
What you have to realise is that you most likely don't need a spot colour for your newspaper. What would you use it for? Would anyone notice the difference?
Is this Spot Plate going to benefit the Newsprint.
Certainly if you're trying to learn about printing and indesign and spot colours and it's free then there's no harm in trying it out. It's free. Everyone love's free stuff.
Just remember though that the colour you see on screen is not accurate, that's why you have the Pantone Books (mentioned first off) that are available to buy, which show the most likely shade of colour that will be printed by the printer, because they should have the same book as you, and the look up that colour reference in their book and they match that colour on the press with the ink that they have.
But it's best to give the Printers a reference for you Spot colour, don't call it “HANKS SPECIAL RED” because they won't know what that means. Use the Pantone Book as a guide and use the reference in the Pantone Book so the printer knows what colour you want.
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