Add colors on a texture using shaders

Newbie & Debugging Questions
#1

First post, yay \o/ :smiley:

Anyway, I couldn’t find a proper solution to my problem, so I’m asking you for help. I wrote a class for displaying text on the screen using anglecode fonts. Now I want also be able to color the text, but when I’m doing the following in my fragment shader, it does not work.

#version 150 core

uniform sampler2D texture_diffuse;

in vec4 pass_Color;
in vec2 pass_TexCoord;

out vec4 out_Color;

void main(void)
{
    out_Color = texture2D(texture_diffuse, pass_TexCoord);
    out_Color = vec4(out_Color.r + 0.5, out_Color.g, out_Color.b, out_Color.a);

    if (out_Color.a < 0.9)
    {
        discard;
    }

}

I expected to see the text slightly red, but it’s still white, as defined in the bitmap. What am I doing wrong here? Do I have to enable GL_BLEND or something first? The code for displaying textures is the same as in the LWJGL Tutorial.