For RegionRenderer, blending can currently be set by renderState.setHintMask(RenderState.BITHINT_BLENDING_ENABLED). This always uses gl.glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA) under the hood (hardcoded).

It would be nice to allow setting other blending functions for RenderState / TextRendererUtil, as we use different blending function in our framework - gl.glBlendFunc(GL.ONE, GL.GL_ONE_MINUS_SRC_ALPHA), for premultiplied alpha, which is de facto standard: http://blogs.msdn.com/b/shawnhar/archive/2009/11/06/premultiplied-alpha.aspx

Currently, I found it hardcoded in the following classes (it even mentions possibility of other functions in comments):

VBORegionSPES2, line 234:
        if( renderer.getRenderState().isHintMaskSet(RenderState.BITHINT_BLENDING_ENABLED) ) {
            gl.glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA);
        }

VBORegion2PVBAAES2, line 607:
VBORegion2PMSAAES2, line 493:

        if( blendingEnabled ) {
            gl.glClearColor(0f, 0f, 0f, 0.0f);
            gl.glClear(GL.GL_COLOR_BUFFER_BIT); // no depth-buffer w/ blending
            // For already pre-multiplied alpha values, use:
            // gl.glBlendFunc(GL.GL_ONE, GL.GL_ONE_MINUS_SRC_ALPHA);

            // Multiply RGB w/ Alpha, preserve alpha for renderFBO(..)
            gl.glBlendFuncSeparate(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA, GL.GL_ONE, GL.GL_ONE_MINUS_SRC_ALPHA);
        } else {
            gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
        }