Some folks on the ludumdare irc channel were interested in how I made the firey particle texture in one project of mine, so here you can treat yourself to the first ever photoshop tutorial by yours truly. Being photoshop, this'll be more of show than tell..
Start off by creating a power-of-two image; I'm using 512x512 here. It's usually better to start at a higher resolution than you'll actually need, as scaling down is easier than scaling up.
Reset the painting colors to black and white, and render difference clouds:
Now, you can re-render the last filter with control-f. Do this a couple dozen times until your texture looks something like this:
Next, adjust the colors using the curves tool.
Tweak the separate channel until the RGB channel looks something like the following. Basically we want to boost red, reduce blue a lot, and tweak green to be low at first but rising high rapidly.
This will result in the texture being mostly red, but the lightest areas turn yellow:
Next, create a new layer, and using the circular gradient tool create a while ball, something like this:
Switch the blending mode of this layer to multiply to make the firey texture fade to black towards the edges, as well as become more circular.
This is already usable, but there's another little trick that will make the fire even more firey. It's subtle, but very effective. Duplicate the 'firey' channel, and apply some gaussian blur to it:
The amount varies, you'll have to play around to find just how much you want to blend. Next, switch the blending mode of this blurred channel to 'lighten'.
This makes the firey thing glow.
Now then, plug the texture into your particle system which rotates and scales quads of the texture and blends them together using additive blending mode, and the result should look something like this:
Do note that since the blue channel isn't completely killed off, the addition will fade from red to yellow to white!
(As always, comments are appreciated).