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.
(Without the model being loaded)
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