Doing a quick skim read of the RAF camo/marking specs it seems the first mention of Desert Scheme is in July 1942 (A.664)
Michael Bowyer (Book 'Fighting Colours') states: "After experiments, particularly at RAE, a new scheme more suited to the desert terrain came into use in August 1941...Some Tomahawk squadrons introduced the new scheme early in August 1941, but in the case of the Hurricanes the 'Middle East' (ie Desert) Camouflage was approved on August 22, 1941".
Its should also be noted that August 1941 was around the time that Fighter Command changes to green and grey camouflage.
Unfortunately this suggests your Hurricane could be in either scheme...however it is interesting to note that the tonal qualities of the camouflage on all 3 aircraft are the same and the underside tone, even the shadow areas, look quite light - which suggests Sky or light grey, therefore it would be unlikely to be Desert Scheme.
In Bowyer's book he has a photo of a Hurricane that looks exactly like yours but without the 'spinach' overspray (same tropical filter, same long range tanks and same light coloured underside, same contrast between the colours of the upper camo), and the caption states "Early Hurricanes to arrive in the Western Desert in 1941 still retained the green/Dark Earth/Sky temperate finish".
The underside is a single tone - the wing is definitely not black.
So I guess that might be strong justification for your choice of the green/brown/sky camo scheme.
Nice model by the way. The overspray is very interesting. I hadn't really considered that they might have actually painted the leading edges light brown before applying the 'spinach' overspray.
Juanita