Questions About Certain JMR Vader Signal Heads

Now I have used various JMR Vader Signals which consisted of anywhere from 1 to 3 heads. Each head has 3 lights. However, I noticed that I also have the option of using a JMR signal that has 3 heads - but only 1 of them has 3 lights on 1 head. The other 2 heads have just 1 light each. What's the meaning of that design? For example: 2 headed signal: Top head (1 light), bottom head (3 lights). Another example: 3 headed signal: Top and middle heads (1 light each) and the bottom head (3 lights). I noticed that the single lighted heads are red but turn off if I throw the switch to go to the siding or diverge to another line. What's up with that? Are those JMR Vader Single Light Heads only meant to be red only? Where can they be used exactly or roughly?

That particular signal would be used at an "end-of-siding" situation, where only a diverging route is possible, such as where a siding joins a mainline. And, since the green and yellow are on the bottom head, that signal can only display either a Slow Clear or Slow Approach indication.

I don't know why but when I use JMR signals, if I have a signal, for example, A 1-3-1 (1 head over 3 head over 1 head) When I put that signal down, then add a safetran signal a distant in front of it, then spawn down a train at the jmr signal, the top light ---^ goes to a blackout, instead of a amber yellow. Why is this?