The link you provided doesn't work
The plasma object isn't the flame object, so it does work a little bit differently. If you paste an object in that has different colours in it, each colour will be blurred and subtracted from, allowing you to create multi-coloured visual effects (such as the example). Maybe with another multiplied map it would be possible to make the colours fade out with a tint rather than just becoming more transparent....so you could make white fade out to a red shade...or you could make all colours tint to black to make a more smoke like effect... I dont know. As for gradients, I plan to add a shader which allows you to use an image and it will take greyscale values of each pixel and map it to the texture...this could then be used by more than just the flame object, however it does require a pixel shader.
When I programmed the flame object for MMF I looped each pixel and mapped it to the image of the gradient in a filter blit. But without a pixel shader, you cant do this in direct X (or at least without major slowdown) so when I write this shader it might only be pixel shader 2 compatible, in which case people using the flame object will need to account for how it might look if people don't have the hardware to support pixel shader 2. Anyway its still possible to achieve nice effects without it mapping to a gradient.
BTW in what way is it hard to use? If you drop the object in the layout and set the background to black it works... I just use a couple of actions to make the shapes in the background move around etc.