In this illustration I'm going to show you how to create objects using multiply layers and gradients.

Start as usual – by creating a new document (1024x768) and a new separate layer (ctrl+alt+n).

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Now use a gradient 2x times with further options:

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X1 result:

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X2
 
result:

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Make a copy of the gradient layer and use some filters on it.
I‘ve used Color Halftone filter with a little bit of Gaussian blur filter.

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On layer set Fill/Opacity and mode:

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We got this:

angelfish illustration