The grey is hard-coded in the SVG pieces, where only 'white' filling (actually #f9f9f9) will be recolored to make the 'black' pieces. The grey (#909090) remains untouched. It should be easy to replace this by another color value with a text editor, though. Would #a0a0a0 do, or should it still be lighter?
An alternative would be to redesign the pieces with some dotted pattern for filling.
The grey is hard-coded in the SVG pieces, where only 'white' filling (actually #f9f9f9) will be recolored to make the 'black' pieces. The grey (#909090) remains untouched. It should be easy to replace this by another color value with a text editor, though. Would #a0a0a0 do, or should it still be lighter?
An alternative would be to redesign the pieces with some dotted pattern for filling.