hehe pinchos on the money but I dont share his corel pimping action.
I have traditionally used photoshop since 2.5 for print/ web and broadcast work. I always use layers and compound layer masks to achieve a variety of effects as well as dodge and burn techniques. Always save the image you want to readjust in your packages native format so it retains all of the layers and so forth then once saved export a file for use in your game. This will save a tonne of time if one little aspect is not quite right and you need to adjust something. Some art packages allow you to work in greyscale and if you layer up the artwork into a series of greyscale gradients you can wash colour into it which allows for rapid reproduction of many instances of the same artwork with different colours. A football team skin would be a good example of this. With one blank jersey you could pump out a lot of different colour combinations. I use the technique for dragon skins as another example. There is a technique as well where you can desaturate a series of layers back to greyscale but its best done if you have the layers already spread out and may take a lot of deep etching path work to secure each component into its own layer.
Instead of using a 2d bitmap type of pixel technique you can use other fine programs that deploy bezier curve paths to create the shapes. Once you the right shapes its a simple matter of colouring them in to suit the requirement.
