The Douglas A-20As of the 18th Squadron NEI were directly from the USAAC and had the USAAC standard paint scheme for that period.
It is not certain whether the aircraft were equipped with Dutch markings (given the very short period this is unlikely).

SchemeColour nameFS numberBS-numberHumbrolXtraColorVallejo Model ColorVallejo Model AirHataka
Douglas DB-7B Boston III: RAF Temperate Land Scheme: Dark Green & Dark Earth in a camouflage pattern for aircraft with a wing span smaller than 75 feet; Sky on lower surfaces.
RAF StandardUpper surfaces Dark Earth   BS:450 29 X002 70.921 71.323 ~206
Dark Green   BS:641 163 X001 70.892 71.324 ~016
Lower surfaces Sky   BS:210 90 X007   71.302 ~026
 Douglas A-20 (delivered to 18 squadron NEI RAAF)
Standard #1 USAAC-schemeUppersides US Olive Drab 41 ~4088   66 X111/X112/X113 70.887 71.016 ~004
US Dark Green 42 (spots) ~4092   149 X114 70.895 71.124 ~019
Undersides US Neutral Grey 43 ~6173   Mix: 1*156 + 1*34 (176) X133/X207 70.992 71.051 ~033

Check www.paint4models.com for an extensive conversion table with lots of colour and paint systems.