Pictures
A few of the sheets the effects load, as the indexed PNGs the build packs.
Each sheet below is the indexed PNG in the repository that the build packs into the game, shown at twice its size. Edit the PNG and its palette, and the next build packs the change. The page on pictures and colours says how an effect finds and decodes them.
quake.c
rushing_strike.c, dragon_cloud.c
target_motes.c
rushing_strike.c