I really like the green flak effect from something my old notes tell me was called "Boomers Flak Pack", for the Shivans... add some EMP, and you're set

.
Once I get my old backups sorted and achtung gets FSMods to have working uploads again, I could upload that pack as I think it's quite useful. (no need for achtung to hurry, it's pretty likely that I'll need more time than he...

)
The contents of the pack were a red, a green and a blue flak effect.
I dunno if that "Boomer" is still active, but I certainly have to thank him for improving my FS experience a good deal

.
And as for why I took the green version instead of the red one:
1) In FS1 cutscenes, Lucy isn't all red.
2) Wasn't there some green in the original maps for the FS1 Shivan fighters??
3) A bit more colour diversity looks a good deal cooler

. (though rainbow-effects would certainly be overdoing it)
4) I like it that that way the flak is discernible from all those Shivan laser blobs flying around.
P.S.: Sorry for necromancing

. I hope that info was at least partially worth it

.