This is the HG Gundam X.
I don't often do patterns that aren't based on a black base coat, so I thought I'd try something different.
I did the full paint job (except for the holographic effect) and some detail painting, like the chest vulcans, with an acrylic brush pen... but I messed up, so I retouched it with a brush.
It was good practice for detail painting with acrylic pens, and for retouching areas where the paint went outside the lines, as it was more noticeable than with a black base coat. (The result isn't great, though.)

HG Gundam X | よっしー's Gunpla works