I've tested this with some visu plugins on a client's project (see plugin list) and it works fine. Put the plugin under the visu ones.
If the setting isn't defined, then it uses the default white color. Make sure that there is a damage sprite setting defined per element, per damage type.
Meaning:
- A 'Thunder' element w/ damage type set to 'HP Damage' uses a different setting as a 'Thunder' element w/ damage type set to 'None'