There is a neat little program called iModelKit installed on my phone. It allows the user to mix paints to match a color. White Ensign Models makes the colors you're interested in. The program will use the White Ensign Model paint as the reference and then use Vallejo Model Air colors to mix. For instance using WEM 5-O Ocean Gray from late 1941, you will use Vallejo Model Air:
71.109 Faded Pru Blue 7 parts
71.111 UK Med Blue/USAF Light Blue 3 parts
71.310 IJN Deep Dark Green2 parts
71.113 IDF Blue/US Intermediate Blue 1 part
You're pretty close with the first color, but adding the other colors it's nearly spot on. Depends on the level of effort one wants to apply.