Not sure if this report belongs here or on the effectlib page, but I've noticed that when setting a spell effect to have particle_override and/or color_override to give it the mage/wand's particle or colour simply doesn't take effect.

It works as intended on effectlib classes other than Modified, so I'm wondering if there's perhaps a specific parameter that needs to be set to make it work?

Same here, only way around this is to try to replicate the effect, but without the Modified class.