There are loads of colour profiles, but the two most widely used are CMYK and RGB.
So here’s the long and short of it: if you’re going to use something on screen, make it RGB. If you’re going to print it, makes it CYMK.
OK? Cool. If you don’t care why but just needed to know that, you can skip to the Resolution bit. If you’re worried someone might one day ask you why then read on.
So what are we talk about? Well, a colour space is ‘a specific organization of colours. In combination with physical device profiling, it allows for reproducible representations of colour, in both analogue and digital representations.’ It’s the thing that maps a colour model. A colour model is ‘an abstract mathematical model describing the way colours can be represented as tuples of numbers (e.g. triples in RGB or quadruples in CMYK). A colour model with no associated mapping function to an absolute colour space is a more or less arbitrary colour system with no connection to any globally understood system of colour interpretation.’ Blah, blah, blah..
‘…What? WAIT, WE’RE NOT GETTING ALL SCIENTIFICAL ARE WE?!’ OK, sorry. What you need to know as a designer is all together it’s how your file, programme and monitor – be it vector or raster, Photoshop or Microsoft paint, phone screen or widescreen TV – saves, displays and allows you to work with any colour information. Obviously when you’re looking on screen or in print at a picture of a leaf, you’re not really seeing the ‘green’ of the leaf, you’re seeing a representation of it – it’s what makes up that representation.
Let’s not over complicate this by getting too much into the dictionary definitions and codey codey geeky geeky stuff. Day to day, this doesn’t overly matter – in much the same way someone making a sandwich doesn’t need to know how the yeast in the bread works.
Depending on the colour profile you’re working in, colours will display differently on screen and also behave differently if you overlaying colours and applying blending modes or transparencies. If you’re working in one and printing in another then what you’re seeing as you work could be very different to what rolls off the press, which might lead to an annoyed client, or (more commonly) a disappointed designer.