Look i have been bored with the old firing color , yellow so i just changed it. you would need txd editor which you can find in gtagarage tools section. Once you have got it extract the textures of weapons open them and there you will see muzzle_texture4 replace it with the one in rar archive. save them. open gta3.img and replace the old files and rebuild it. done. run game get a gun fire it enjoy the new color.
Some may have thought why i have uploaded just one file , its because many have different types of gun and they don't want to lose it , that's the reason why i have uploaded one file & please comment & rate

Guess what you can also ask for colors . Don't hesitate just comment or PM

Made 9 Textures.

I cant make a non crazy version but found a way
you would need g-txd select muzzle texture 4 and replace it with this texture and select alpha used and then use original alpha