The signal shown in Foghuts picture is a 4-aspect junction signal. Working from the top the lights on each head show yellow, green, yellow, red where green=clear, both yellows=preliminary caution(i.e. next signal showing yellow), lower yellow=caution(i.e. next signal showing red) and red=danger stop.
I think that this type of signal is more suited to routes with high traffic flows and that your layout would only require 2-aspect or possibly 3-aspect signals (i.e. red and green, yellow and green or red, yellow and green)
In your double-slip example the main signals controlling entry into the tunnel would be placed further back. One between the Virgin 57 and white van at the end of the double-track section and one on the line coming from the traverser. I would suggest that both were able to display red, green and yellow.
Did you have any particular scenario in mind when you incorporated the double-slip and the hidden siding into your plan? To me it gives the impression that the tunnel was once double track and that the engineers are in the process of simplifying the trackwork and haven't yet got round to removing the double-slip.
