The surface of most of the ground is an animated red neon road, sometimes held up a little way by thin blue bars, other times surrounded in little flashing decorations, around loops and curves.
The amount of variety you'll see is incredible, and way too much to be detailed here (conveniently). Amongst the gold blocks there are colourful signs depicting arrows, flowers, bars and crazy shapes, and little panels that alternate between images of Sonic and star, and Tails and moon, respectively. Most of the ground is of a gold colour, made up of many small blocks and square black gaps, possibly to indicate windows on buildings, but all over the place you'll also find all manner of flashing, neon decorations.