"J3 leaning slightly towards amber colour"

I haven't tried it myself but judging from these pics of an excellent Canberra model (scroll down) Xtracrylix XA1016 RAF Hemp might be a good contender for "J3 leaning slightly towards amber colour" out of the bottle. In terms of an approximation it is a much better starting point than Humbrol 90 Matt Beige Green.

A comparison was drawn here with mentions here and here. The hobby paints for this colour do seem to vary quite significantly so some additional tinting with small amounts of green and/or yellow ochre might be required.

Update

Since blogging this I have painted out a swatch of Humbrol 168 (nice to brush paint too) and compared it to the replicated Zero paint colour. It's not a precise match and a little 'creamy' - something is missing - but for practical purposes, considering scale and for the convenience of an out-of-the-tin enamel easily available at the LHS it is a reasonable choice for the modeller, especially on a 1/72nd scale model. If Humbrol 86 Matt Light Olive is added to make it more greenish only a tiny amount is required, just a dash really; whilst to represent the more amber tones of the Nakajima-built Zeros Humbrol 225 Matt Middle Stone can be added. While I was at it I also compared a brushed out swatch of Humbrol 90  Matt Beige Green (= RAF Sky), recommended by Airfix for their new Zero model, and can confirm it is nothing like the proper colour, about as far off as far off could be. They should have suggested 168 and finally bucked the misinformation trend.