The neon sign is interesting for its use of color with an opacity map. Simply, a full color image was viewed through a neon effect made in Photoshop. Just save your color image with the grayscale as a separate channel in Photoshop and import it into Bryce, which will automatically assign the grayscale as an opacity map. If you don't have Photoshop, simply import the color image, select Opacity Map and then Paste your grayscale into place.