There are many parameters to tweak in each of these flames. They all use direct color, usually via dc_linear variation; adjust the scale parameter to see the color gradient expand and contract through the flame.
The flame with harmonograph_js is very sensitive to seed variable changes. Tweaking the other harmonograph parameters change things too. Some have useful ranges of just a few numbers; others will take adjustments in the 1000s or 10000s.
In the juliascope3Db and polarplot2d_wf flame, polarplot2d_wf has several preset_ids and several other effective parameters you can adjust. Juliascope3Db’s power can be infinitely adjusted, but works best with integers. The dist parameter can also really change things up as will playing with the other parameters.
The other flames follow the same adjustments, presets and various parameters to try.
Experiment! All the picture examples were rendered with the CPU, although all, except the multi-layer one, can use GPU too.