Getting alpha to work

Newbie & Debugging Questions
#1

Very simple question here

I’m trying to draw a transparent gray rectangle over the entire screen
This draws the gray rectangle:

glColor3f(.2f, .2f, .2f);
glRecti(0, 0, DISPLAY_WIDTH, DISPLAY_HEIGHT);
glColor3f(1f, 1f, 1f);

Now how do I make it transparent?
Adding this to the front did nothing:

glAlphaFunc(GL_ALWAYS, .5f);

Thanks

#2

Enable blending (i.e. at initialization):

GL11.glEnable(GL11.GL_BLEND);
GL11.glBlendFunc(GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);

Then use the alpha component:

glColor4f(.2f, .2f, .2f, .5f)
#3

It works, thanks