There are two key colour modes to be aware of in digital design; RGB & CMYK.
RGB: Red + Green + Blue
Use for: Screen (web, email, presentation, CD ROM, moving image).
Some high end photographic printers.
Pros: Produce a wide range of colours including very luminous hues.
Cons: Can’t send to offset print.
Difficult to colour manage.
RGB are referred to as additive colours as white is created by adding all these hues of light together.
CMYK: Cyan + Magenta + Yellow + Black (key)
Use for: Print (offset, laser, inkjet, digital).
Pros: This colour format is the most frequently used in variable colour printing. Print runs are typically cheap as machines are set and ready to go.
Cons: Difficult to colour manage.
Difficult to reproduce RGB colours.
Cannot produce metallic or fluorescent effects.
Larger file size.
Can’t display on screen.
CMYK are also referred to as subtractive colours as white is created by subtracting all coloured inks from the page.
This article explains how to fix strange colour shifts when exporting images for the web
The Mysterious “Save For Web” Color Shift
Creating great colour schemes from scratch can be difficult. Adobe’s Kuler website is provides a variety of methods to assist with this. Start by searching the massive and ever expanding user submitted database by keyword. For example, if looking for a nature inspired colour scheme type “forest” into the search engine to be presented with almost 2000 pre-made swatch groups. Alternatively upload a photo from your computer or enter a URL and Kuler will generate a range of colour schemes automatically. Kuler is also a great way to work with (and learn) colour theory rules. Signing in with your Adobe account allows you to save your theme, upload it to the online community and download a Swatch Exchange file to import into your Adobe programs or send on to others. You’ll need an current version of Flash player for your browser to us Kuler.