There has been a rash of blank ink pads so you can make your own 'custom' blends. It does not quite work like that really - but it is a fun way to create something a bit different.
I picked up the big Dylusions pad ages ago - the bigger the better for this really.
Spritz a couple of colours onto the pad and use a big bold background stamp to pick up the mixes of colours and stamp. You will find that you get all sorts of extra colours where the inks have blended together and made new shades - I have purples - greens and navy in the stamping. Just give the ink pad a good wash under the tap to get the ink off - you can pat it directly onto paper for another effect.
You can't see all the detail really - I have used quite a bit of silver and white