I've been looking for that functionality for years. If it is there it is well hidden. I'd also like to just be able to change the font and color of a single equaiton without changing the rest. I get the feeling that PTC isn't putting a lot of resources on MathCad and pretty isn't on their agenda at all.
There are a number of discussions on ways of (almost) achieving this on the mathcad collaboratory. But nothing as direct as you get with excel's conditional formating...
Use visual basic script. It shows red/green like you want
but unfortunately doesn't print it. MathCAD needs to fix.
the VB script that controls the display of Text Box 2
Sub TextBoxEvent_Exec(Inputs,Outputs)
If Inputs(0).Value > Inputs(1).Value And Inputs(0).Value < Inputs(2).value Then TextBox.BackColor = vbGreen
TextBox.Text="GOOD"
Else
TextBox.BackColor=vbRed
TextBox.Text="BAD"
End If
End Sub