Monocock,
You really should go to a Gliding club for a chip removal session.
Colour:- Most modern,(glass), gliders are white, so are an awful lot of modern light aircraft for the same reason. Gliders are usually either turning in a thermal, in which case they are easily seen due to the sun glinting off the wings,(assuming you are spending more time looking out than admiring your GPSDMEVORHDI), or they are flying 'on track' in which case their speeds are similar to most powered aircraft and the glider pilot has probably seen you anyway.
Exit areas:- Gliders do not generally enter controlled airspace so they will tend to be 'crushed against the fence' so to speak. If you are cleared to operate in airways, stay in there where it's nice and safe and cozy and leave the open airspace to those of us with eyes. Glider pilots don't know about VOR and wouldn't know where to find one to cluster around it in the first place. I suspect you are seeing gliders when you start doing a proper lookout, i.e. when you leave controlled airspace or approach a VOR and think "dodgy area, this, I'd better have a look out of the window."
Radio:- Most gliders are on Radio but they are on 130.4 or 130.1 or a few other dedicated glider frequencies. They have never heard of 123.4. Unfortunately, they also do not generally carry lists of frequencies and tend to get busy low down which is why they may land at your airfield without making any radio calls. In most cases it would be illegal for them to do so as they do not have radio licenses and are only allowed to use the gliding frequencies.
PR:- 99.95% of the general public have never seen a glider in the air. Non air-minded people do not look above head height unless a noise causes them to look.
I cannot remember the last Glider/Power mid-air and I will just about guarantee that the power aircraft concerned would have been a glider tug.
Mike W