The P-40E's were originally meant for the USAAC and had the standard USAAC paint scheme scheme applied. The Dutch red-white and blue flag was painted over the US markings on fuselage and undersides of the wings.
The rest of the US markings were painted over, most probably with available paint, such as "Donker Blad": The flag was also applied on the under surfaces of the wings.

The Curtiss P-40Ns initially also had the standard USAAF colour scheme of olive drab over neutral grey.

Scheme Colour name FS number Humbrol XtraColor VAllejo ModeColor
Standard #1 Upper surfaces US Dark Olive Drab 41 ~4088 H66 X111/X112/X113 70.887
US Medium Green 42 (spots on some P-40N) ~4092 149 X114 70.895
Undersides US Neutral Grey 43 abt ~6173 Mix: 1*156 + 1*34 (H176) X133/X207 70.992

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

Curtiss P-40E-SMALL
Colour scheme Curtiss P-40E NEIAF, February 1942.

 

Below some examples of colour schemes of the Curtiss P-40N. Per individual aircraft this may differ, depending on the period, but also from the pilots, who often gave a name to their personal aircraft.

Both  "Dutch Profile" issues, written by ax Schep and Luuk Boerman you may find a large quantity of photographs and lots of colour profiles.

Curtiss P 40N 8 SMALL
Colour scheme Curtiss P-40N 120 squadron NEI: Blue patrol; Flags and white, sometimes medium grey aircraft letter.
Curtiss P 40N 7 SMALL
Colour scheme Curtiss P-40N 120 squadron NEI: Yellow patrol; Flags and white, sometimes medium grey aircraft letter.
Curtiss P 40N 6 SMALL
Colour scheme Curtiss P-40N 120 squadron NEI: Red patrol; Flags and white, sometimes medium grey aircraft letter
Curtiss P 40N 5 SMALL
Colour scheme Curtiss P-40N NEIAF 1948: Flags replaced by Dutch roundels. Part of camouflage paint is removed. This differed per individual aircraft
Curtiss P 40N 4 SMALL
Colour scheme Curtiss P-40N NEIAF 1947: Flags had an white border applied. Part of camouflage paint is removed. This differed per individual aircraft
Curtiss P 40N 3 SMALL
Colour scheme Curtiss P-40N NEIAF 1948: Flags replaced by Dutch roundels. Part of camouflage paint is removed. This differed per individual aircraft
Curtiss P 40N 2 SMALL
Colour scheme Curtiss P-40N NEIAF J-320 PVA, 1950. Aircraft completed stripped of paint, though some parts (anti glare) still in (faded)  Olive Drab ANA 613.
Curtiss P 40N 1 SMALL
Colour scheme Curtiss P-40N NEIAF, 1949 - 1950. Aircraft completed stripped of paint, though some parts (anti glare) still in (faded)  Olive Drab ANA 613. Differed per individual aircraft.