I'm working on a modification for Lemur that will allow one to create panel backgrounds by writing them in their style definitions rather than using a texture. Currently you can create a background, such as for a button or window, and specify the radius of the corners, a border thickness, a border color and an internal color or gradient with up to eight colors which can have their positions within the gradient specified as a percentage. By default a gradient goes from bottom to top, but can be rotated to achieve left to right or diagonal. The border can also have a gradient, but just two colors for now.
The rounded corners are achieved using the same technique I used to make jME-CircleShader so the edges are anti-aliased in the shader without requiring hardware or post-process anti-aliasing. Because borders and gradients are drawn by the shader, rather than a texture, these are fully scaleable without becoming pixellated.
P.S. I also got it so you can use both the original bitmap fonts or true type fonts through jME-TrueTypeFont. Also working on improvements to, hopefully, make it so you can create a single UI that will scale seamlessly between desktop and Android devices.