Combinations of mathcolor and mathbackground.
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"> <mrow> <mroot> <mi>a</mi> <mn>3</mn> </mroot> <mo>,</mo> <mroot> <mi mathcolor="#FF0000">a</mi> <mn>3</mn> </mroot> <mo>,</mo> <mroot mathcolor="#FF0000"> <mi>a</mi> <mn>3</mn> </mroot> <mo>,</mo> <mroot mathbackground="#80FF80"> <mi>a</mi> <mn>3</mn> </mroot> <mo>,</mo> <mroot mathbackground="#80FF80"> <mi mathcolor="#FF0000">a</mi> <mn>3</mn> </mroot> <mo>,</mo> <mroot mathcolor="#FF0000" mathbackground="#80FF80"> <mi>a</mi> <mn>3</mn> </mroot> <mo>,</mo> <mroot> <mi mathbackground="#80FF80">a</mi> <mn>3</mn> </mroot> </mrow> </math>
Author: Bruce Miller