The grey looks OK, rather like the colour known as 'Mixed Grey', which was slightly lighter than Ocean Grey, and used for a short period, although not normally on Tempests. It might be that the green looks rather ...er... green, compared to RAF Dark Green. This could be making the grey look darker.
There were four inch yellow tips on the props of all RAF aircraft. Any photo where it appears the tips are not yellow, will either be due to exposure of the film, lighting angle, or maybe wear and tear.
The yellow wing leading edge I.D. stripes were present from 1941 on all single-engined RAF day fighters, although by around march 1945, certainly in 2 TAF, these were often removed. However, for the period of your model, they would be in place.
Sorry, I don't normally model in 1/72nd scale, so can't advise on which are the better Spitfire kits.