I have had a yellow light for a week now - the Virgin help page doesn't even mention a yellow light.
Yesterday I tried to run a test, it got to 30% then said "we're trying to sort it out, come back in 10 mins" I came back the page had gone blank and when I refreshed it said "we can only run 3 tests a day - come back tomorrow"
I've located your details and there appears to be an SNR fault present within your area under the ticket reference F006506661, with a review currently set for 14 SEP 2018. You might find that your Virgin Fibre, Virgin TV or TiVo® services are intermittent, with the picture freezing or disappearing now and then. We are sorry and our engineers are working hard to resolve this for you.