libdgx - Mesh Shader Blending Errors

Hi, I just don't get why the blue triangle is rendered, I think that Blend isn't enabled but I don't know what I could do to fix it.
You can just compile and test it on your own if you want to, the code is "working", the shaders not Roll Eyes

What I got:

-a blue triangle
What I expected:
-a red triangle, because the opacity from the blue one is 0

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import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.backends.lwjgl.LwjglApplication;
import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.Mesh;
import com.badlogic.gdx.graphics.VertexAttribute;
import com.badlogic.gdx.graphics.VertexAttributes.Usage;
import com.badlogic.gdx.graphics.glutils.ShaderProgram;

public class ErrorShader implements ApplicationListener {
    MeshHelper meshHelper;

    public static void main(String[] args) {
      LwjglApplicationConfiguration cfg = new LwjglApplicationConfiguration();
      cfg.title = "Error";
      cfg.useGL20 = true;
      cfg.width = 500;
      cfg.height = 500;
      cfg.resizable = false;
      new LwjglApplication(new ErrorShader(), cfg);
   }
    
    
    @Override
    public void create() {
        meshHelper = new MeshHelper();
        meshHelper.createMesh(new float[] { -1.0f, -1.0f, Color.toFloatBits(0, 0, 255, 0),
            0.0f, 1f, Color.toFloatBits(0, 0, 255, 0),
            1f, -1.0f, Color.toFloatBits(0, 0, 255, 0) });
    }
    
    

    @Override
    public void resize(int width, int height) {
    }

    @Override
    public void render() {
        Gdx.graphics.getGL20().glClearColor(0.2f, 0.2f, 0.2f, 1);
        Gdx.graphics.getGL20().glClear(GL10.GL_COLOR_BUFFER_BIT);
        Gdx.graphics.getGL20().glEnable(GL20.GL_BLEND);
        Gdx.gl.glBlendFunc(GL10.GL_ONE_MINUS_SRC_ALPHA, GL10.GL_SRC_ALPHA);
        meshHelper.drawMesh();
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }

    @Override
    public void dispose() {
        meshHelper.dispose();
    }
}

class MeshHelper {
    private Mesh mesh;
    private ShaderProgram redShader;
    private ShaderProgram blueShader;

    public MeshHelper() {
        createShader();
    }

    public void createMesh(float[] vertices) {
       mesh = new Mesh(true, vertices.length, 0,
               new VertexAttribute(Usage.Position, 2, "a_position"),
               new VertexAttribute(Usage.ColorPacked, 4, "a_color"));
        mesh.setVertices(vertices);
    }

    public void drawMesh() {
        if (mesh == null)
            throw new IllegalStateException("drawMesh called before a mesh has been created.");
        
        redShader.begin();
        mesh.render(redShader, GL20.GL_TRIANGLES);
        redShader.end();
        blueShader.begin();
        mesh.render(blueShader, GL20.GL_TRIANGLES);
        blueShader.end();
    }

    private void createShader() {
       String vertexShader = "attribute vec4 a_position;    \n"
                + "attribute vec4 a_color;       \n"
                + "varying vec4 v_color;         \n"
                + "void main()                   \n"
                + "{                             \n"
                + "   v_color = a_color;         \n"
                + "   gl_Position = a_position;  \n"
                + "}                             \n";           
       

       String fragmentBLUEShader = 
             //GL ES specific stuff
               "#ifdef GL_ES\n" //
             + "#define LOWP lowp\n" //
             + "precision mediump float;\n" //
             + "#else\n" //
             + "#define LOWP \n" //
             + "#endif\n" + //
             "\n" + 
             "void main() {\n" + 
             "   gl_FragColor = vec4(0.0,0.0,1.0, 0.0);\n" +  //Why is that rendered?
             "}";
        blueShader = new ShaderProgram(vertexShader, fragmentBLUEShader);
        if (blueShader.isCompiled() == false)
            throw new IllegalStateException(blueShader.getLog());
    
        String fragmentREDShader = 
             //GL ES specific stuff
               "#ifdef GL_ES\n" //
             + "#define LOWP lowp\n" //
             + "precision mediump float;\n" //
             + "#else\n" //
             + "#define LOWP \n" //
             + "#endif\n" + //
             "\n" + 
             "void main() {\n" +
             "   gl_FragColor = vec4(1,0,0,1);\n" + 
             "}"; 
        redShader = new ShaderProgram(vertexShader, fragmentREDShader);
        if (redShader.isCompiled() == false)
            throw new IllegalStateException(redShader.getLog());
    }
    public void dispose() {
        mesh.dispose();
        blueShader.dispose();
        redShader.dispose();
    }

}

edit:
Got it, if I use

1	Gdx.gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);

it works,
but I don't understand why the other one doesn't work. It would be great if someone could explain it
The text is german but the pictures are nice: http://wiki.delphigl.com/index.php/glBlendFunc#Beispiele

thx for help,
best regards