I'm using GLModel (http://potatoland.org/code/gl/) to load models with textures.
If i try to draw lines with plain color (glColor3f), they appears black.
(http://img849.imageshack.us/img849/3088/probe.png)
(Without the model being loaded)
(http://img836.imageshack.us/img836/8711/expect.png)
without looking at any code, its likely you need to disable textures (or lighting) before drawing the lines.
e.g. by calling
GL11.glDisable(GL11.GL_TEXTURE_2D);
That's what I was looking for. Thanks ;D