In simplified terms, on the Spitfire MkII (Mark Two), for this parerticular scheme, the spinner and the rear fuselage 'FighterID' band should be finished in Sky, more than likely supplied by most model paint companies as 'Sky Type S', or the equivalent. This, as both Antoni and Wojtek have indicated, is the shade that leans towards a green hue, and actually looks like a whitish cream colour. Since the demise of Humbrol as we knew them I have normally mixed my own shade, using matt white, a spot of yellow, and a spot of blue, until it looks more or less right!!
For some strange reason, very few kit manufacturers are able to supply decal code letters in the correct shade, as I've seen bright green, an almost buff colour, cream, greyish green -all sorts!