Incorrect answer. I went ahead and bought the US Vertical (1st) edition and it has plain white spines with BUDDHA written down them and a coloured band the colour of the front image (red, blue, yellow, dark green, orange, purple, lime green, sky blue in ascending order) with the number of the volume at the bottom. Very ugly in comparison to the UK picture edition. Alas, volumes 2, 3 and 4 of the UK edition are out of print, hence my purchasing the Vertical edition.
The hardback Vertical edition is printed with picture spines, though some volumes have limited availability and require protracted hunting. If you have the time and cash to invest in these they look way nicer on the shelf. Here's hoping Harper Collins decide to reprint their paperback edition (with illustrated spines) again.