I have a lightly-colored Grease Pencil Stroke with Line Art modifier, but it appears with dark color in render.
Please have a look at this file (Blender v4.0.2), then run the Render > Render Image command to see the difference between the color of the stroke in 3D viewport and in render window:
Looping_Road.blend (1.4 MB)
How to render the stroke with its light color?