The fountains in Sheffield city centre are to be dyed yellow to celebrate 100 days until the Grand Depart.
The event, called Painting the City Yellow, is part of the Yorkshire Festival.
Yellow has been chosen because it is the colour of the Tour de France winner’s jersey.
Terry Wragg, a visual artist and one of the three organisers, said: “The event is potentially spectacular, and definitely non- toxic.
“This dye is incredibly strong, and the science behind the fluorescent effects is fascinating.
“It has been impossible to carry out any dress rehearsal, for obvious reasons, so anything could happen. We are doing it for fun, and hope people find the effects enjoyable.”
The dye, called fluorescein, is normally used in science and medicine.
After dark, bright lights will be projected onto the Peace Gardens fountains to turn them luminous.
There will be ultraviolet torches available so people can create the effects themselves and the fountains will remain yellow for two weeks.
The project has been funded by Arts Council England, local businesses and Sheffield Council.
The dye will be put into the Barker’s Pool fountains at 1pm and the Peace Gardens’ fountains tomorrow, at 2pm.