I was able to modify the GS_ShieldImpact.fx so that the shield hit effects are more visible - right now the shields are really visible, allmost opaque when under heavy fire, and this can be adjusted at need.
You do that by adjusting the color.alpha value in the line (two of them):
oColor0.a = lerp( 0.1f, 0.f, dist/g_ExternalHitRadius);
just increase the first value - the above opacity was achieved by setting it to 0.8f
The problem is with adjusting the impact effect itself; it seems to be unrelated to any texture file, instead calling a procedural effect, or constants which are hardcoded (or unknown to me) - the prime suspects being the two texture calls:
texture g_TextureEnvironmentCube : Environment;
The effect is that the shield color is shiny - by adjusting the alpha to the extreme, it turned out the shield envelope has the same mirror finish as objects with maxed reflection. By altering the following line in the GetPixelColor procedure:
float4 color = environmentColor;
float4 color = g_GlowColor;
we enable the shield to glow with the color defined in the shield section of the player .entity file (Vasari, which I used for the template race for the Xin apparently have green shields):
All that remains is to find out how to change the impact effect itself.