OpenGL override scene transparency

Question

I'm using GL11 in Java, and the current issue I'm facing is blending. I'm making a simple fade-out animation, and as shown in the image, the borders of the rectangle are darker because they've drawn over the background. How can I override an entire scene to be at one transparency level? Apologies if this doesn't make sense, I'm new to OpenGL.

My code:

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
DrawUserInterface(x, y); // Simple vertex rectangles