How come when i manually change the alpha value in array, being passed to shader, the result is the same for both 0.0f and 1.0f ?

I was expecting the object to be drawn with some level of transparency, depending on alpha value.

I'm not using any textures. I always see my red object against a black background.

accessing glsl variable from java ..

float[] color = {1.0f, 0.0f, 0.0f, 1.0f}; gl2.glGetUniformLocation(shaderProgram, "vColor"); gl2.glUniform4fv(mColorHandle, 1, color, 0);

glsl , fragment shader ..