Single color doesn't mean monochromatic, though. Keep that in mind. While the aircraft may have only had one color used on the upper surfaces, there are different shades within that color that can be combined. For example:
OD fades different ways. Note in the lower right corner the fabric covered control surfaces have a paler, slightly more faded look to them. Subtle, but it is noticable. Note, also, that the OD fades from the point of application, but when parts are serviced, repaired, or replaced, that the fresh paint put over them, or the newer (less weathered) parts are different shades. In this case they appear as a darker spot on the right-most plane from the canopy to just behind the cockpit. Apparently that area was retouched with fresh (or... fresher) paint. Looking at the lower/middle plane, we see the top panel of the engine cowling, underneath the tiger's head, is darker. This and many engine panels are traded out as they get damaged or dinged, and may have different shades denoting new-ness or aged-weathering. Then we also have wear patterns on the wing roots, as well. They don't always show through to the metal. Sometimes the paint is scuffed to look lighter (scratched/scraped), and sometimes it is worn smooth or polished by constant servicing (laying/sitting on the wings to access gun bays, etc) and may appear darker.
So, don't be disheartened by the fact the plane you want only has one color. You can still make it look very interesting!
