mpadded_colors

mpadded with mathbackground.

W3C sample	WIRIS
	$$a+b+b+a$$

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>a</mi>
    <mo>+</mo>
    <mpadded width="+1em">
      <mi>b</mi>
    </mpadded>
    <mo>+</mo>
    <mpadded width="+1em" mathbackground="#80FF80">
      <mi>b</mi>
    </mpadded>
    <mo>+</mo>
    <mi>a</mi>
  </mrow>
</math>

Author: Bruce Miller