Simple shader writting

Hi there!

Given skeletal mesh with different materials along its vertex groups.
How do i write the simplest shader in unreal
color = vec4(0,0,0,0);
for one of the materials ?

This shader should not interact with anything else in the scene,
simplest constant color shader.

so far im using the regular UI material interface Im not able to get this behavior and the mesh it self cast shadows or generate other artifacts.

any help will be great !