Stranded has multiple smaller wires within each insulator and is more flexible and resistant to breakage. Solid wire will easily break if it has been crimped, or is bent too often. Much of the 4 or 6 pair network and 2 pair telephone wire that you might find surplus, or in your garage, is generally solid. It is OK to use this wire, but only for sensors that are permanently installed where the wire will not be moved or bent often. The use of multiple conductor cable is recommended.
Some sensors require power.
With a 4 pair cable, you could use one pair for power, and the remaining three for measurements. By the way, color does not matter. Most multi conductor cable has a gray or beige outside coating with different colors used for each of the interior wires. Be sure to check with your local authorities to learn what requirements they have for cabling. This is especially true for wire installed in the under floor, or ceiling, wiring racks, of commercial buildings.