There should be something that you can create a gradient, I'm pretty sure it has a rainbow colored one, you can use that, I don't have photoshop anymore so i don't remember much about it
Perhaps if you gave us a better idea of what you want to use it for .. for example, a full screen abstract .. or .. just a smaller piece of the whole .. It's possible you might be happy with a kaleidoscope effect .. perhaps with a little gaussian blur to simulate the 'bleed' of the dye ..
Assuming you have a more recent version of Photoshop .. create two or more full screen layers of nice kaleidoscope images, using different, but complimentary colors .. then, using the layer styles, blend them using whatever gives you the effect you're looking for .. if this begins to give you the results you are looking for, don't be bashful about throwing a couple full color layers into the mix and blending them as well, using the layer styles
kaleidoscope is a FREE plugin (as are all the items listed on the left, except the top one) .. feed it anything and it will spit out a mangled version of it ..
back to the Gaussian blur .. if you duplicate a layer, so that you now have two, apply a Gaussian blur of, maybe 5 - 10 to the original (bottom layer) and set the top layer to OVERLAY in the layer styles .. and you will have a "soft-focus" special effect .. suitable for almost any portrait or picture .. if you like soft-focus .. not everybody does
Beyond Posterization @ wetzelandcompany .. probably not what you want .. but interesting nonetheless .. an example of 'the sky's the limit' when blending stuff