Sorry to say that you will not be able to do this without conditional formatting. To do this will require some fancy coding using the OnContextChange event and a lot of conditional formatting. All other DOM events you can normally use in HTML are locked out in InfoPath for security reasons.

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Greg Collins [InfoPath MVP]
Please visit: http://www.InfoPathDev.com
Hi all,
Does anyone know how to apply a colored shading to the active element (ie:
The textbox that currently has focus) in an InfoPath form? As the user tabs
around my form, I want the background of the active textbox to be shaded
yellow.
Since my form is huge and changes frequently, I'd like to find a way to do
this without using conditional formatting on each textbox--perhaps by
applying a css style to the view (.xsl file).
Thanks in advance.
--Peter Ghali