For brush painting I use mostly Model Master Acryl colors, as they are easiest to work with. I wanted to use them for painting the aforementioned nationals, but I don't want to make them too pale or too dark. In fact, I'd like a subtle variety of skin tones, as my upcoming diorama has both Chinese and Japanese.

You might want to take a look at the following article on painting different types of ethnic skin tones. I found it very helpful on choosing a range of paints to do my African American faces. The paints referenced are Vallejo, but I'm sure you could easily adapt to similar colors in the Model Master range.

http://www.coolminiornot.com/articles/1310

I remember seeing that article in the past. Thanks for finding it again!