Hmm, the following code is from a shader I've made and it works:
Code:

// C-script:
var SunColor[4] = 0.8, 0.8, 0.7, 1.0;

material* TempMaterial;
function SetMtlSunColor(mtrl)
{
	TempMaterial = mtrl;
	TempMaterial.skill1 = float(SunColor[0]);
	TempMaterial.skill2 = float(SunColor[1]);
	TempMaterial.skill3 = float(SunColor[2]);
	TempMaterial.skill4 = float(SunColor[3]);
}

..
SetMtlSunColor(mtlMatte_20_H);
SetMtlSunColor(mtlShiny1_20_H);

// HLSL:
const half4 vecSkill1;
..


shader tutorial