Getting hold of the colour info from japanese kits is very simple, anything besides Tamiya usually refers to Gunzes 2 colour ranges:
They are usually marked as follows "H-8,8 Silber" where "H-8" is the colour in the Hobby Colour range(Aqueous Colours), and the "8" is the same colour in the Mr. Colour Range.
Another example:
H-90, 47 Clear Red.
Downloading one of the many Gunze colour charts available online also help as you can match the kana.
Here is a link to an english chart of the gunze aqueous colors:
http://www.plastikmodell.de/html/gunze_color_chart.html
Another useful link:
http://www.hlj.com/~tanoue/HLJ/colorname.html
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Found the ling for the japanese charts too:
Mr Color:
http://www.rainbowten.co.jp/english/emcolors.jpg
Mr Hobby Color
http://www.rainbowten.co.jp/english/emcolor1.jpg
Mr Spray:
http://www.rainbowten.co.jp/english/emcolor2.jpg
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HTH.