A very early de-luxe Ruby - the London registration number dates from July 1934, the same month the model was introduced. Most ARQ Rubies have black window surrounds, this one appears to hve the surrounds in colour, possibly a contrasting colour to the main body. This sort of colour scheme was favoured in the early sales brochures, but this photo is the first evidence I have seen to suggest that some cars were turned out like this.
It is worth considering that black and white photographs don't always represent colour tones as one might expect, therefore I anticipate it is possible a very dark grey may look lighter?
BGC ran from June '34 and CGC started Aug '35 - so this car - being no 948 of 999 - could have been registered later? - say Summer '35? - or would they have raced through the BGCs and then had a break (using other letter codes) before starting the CGCs?
The notes I have suggest BGC was completed in the month of first issue, ie June 934, so I was guessing that it ran through to early July. After BGC London issued more B-prefix sequences, BGF, BGH and BGJ all in June 1934, then BGK,N,O & P in July, BGT,U & W in August, and so on. The last B-prefix London issue was BYY in July 1935, before starting with the C-prefix sequences.