Hello Jon,
You can either enter the style as Princy mentioned or you can could just do this:
I added the RadInput and RadInput_Default (if you're using the Default skin, you will need to change it if using another skin or if using the RadSkinManager you could change it to this "
RadInput_<%# Container.Skin %>") classes to your label cell, so that the correct styles are applied to your label and they match the one used by the actual RadTextBox label.
I hope that helps.