To implement:

create 6 sets of ChartProperties, each with different background colors, per-series colors & fonts
take 6 screenshots of a Column or Pie chart using each of the themes
use screenshots to create a thumbnail image for each theme (stored in resources)
place 6 theme thumbnails in CSplitButton dropdown (in toolbar)
on selection, update ChartProperties with colors & fonts from selected theme
 

From Matt :

[x] 7922 themes
    [x] reduced light brightness (to avoid white-washing the image)
    [x] default + 5 other themes: Ocean, Dawn -- Hot, Cold, Light on Dark
    [x] theme properties
        [x] backgroundcolor top/bottom
        [x] per-series colors
        [x] getFillGridColor
        [x] font color (value axis title/label, category axis title/label, series axis title/label, chart title color, data label color)
        [NA] font size (legend, series, category, value, title, axis title, data label)
        [NA] font

[Deferred] 7892 horizontal axis labels

I don't see how to use these.  I am assuming from the toolbar, but I don't see any buttons for this.

These appear in toolbar when u're creating a chart based off "Grid" result. However, these do not appear when u're creating a chart based off "Pivot Grid." I consider this a bug.

fixed long ago