I started originally with a pattern style that I've used for another project - the green swirly pattern and added these pinky/orange trims to the M4A4 model
Then I layered them over each other and colour corrected a little bit so it didn't look like a bright fluro watermelon gun and used a clipping mask so it was only over the M4A4 UV chart
And using that image ^^ as the VTF we end up with this result: