Ambient light not working with object color

I’m trying to add very basic ambient lighting using custom HLSL but the final pixels don’t seem to take into account the object’s color.

float4 mainPS(float4 Color:COLOR0) : COLOR0
	float4 objectColor = float4(1.0f, 0.5f, 0.31f, 1.0f);
	float4 lightColor = float4(1.0f, 1.0f, 1.0f, 1.0f);
	// ambient
	float ambientStrength = 0.1;
	float4 ambient = mul(ambientStrength,lightColor);
	float4 pixel = mul(objectColor, ambient);

	// return objectColor;
	return pixel;

So if I just return the objectColor, the object will be rendered as orange but if I return the objectColor multiplied by the ambient light, it will come out black with white ambient light.

edit: thanks PumpkinPudding, all I had to do is: float4 pixel = objectColor + ambient;