Is it possible to alternate the glow effect colors in ammo particles, so that each bullet is a different color from the last?
Thanks in advance.

With only ini code, no. Ini could would allow you a maximum of two different colors (Round and Tracer).

You would have to use Lua to create bullets - the gun itself fires what is referred to as a "null" bullet, which is a projectile with the same mass and velocity as it's intended to shoot, but HitsMOs = 0 and with a short LifeTime (5 or something).

The gun would then have a script that checks whenever the gun is fired, and then spawns a specific colored MOPixel at the gun's muzzle and throws it in the direction that the gun is facing.

Dummy.rte/Devices/Weapons/Annihiliator.lua

has an example of a gun that uses Lua for spawning projectiles, which you can use as reference, but you'll have to trim it down a lot to get rid of the charging mechanic.

I'm guessing it's also possible to have each bullet alternate colors from a set selection? through Lua I mean.

Yup. You'd need do define a MOPixel in ini for each specific color that you'd want, and then the script would control which MOPixel to spawn for the bullet.

Awesome, thank you! You're always so helpful to me.