There are three useful options
One color, one job. Choose it for prototypes, hidden brackets and objects you intend to paint. If the design allows it, you can also print differently colored pieces separately and assemble them. That trades automatic color changes for assembly work.
A manual change at a chosen layer. Try it for raised lettering or color bands. The slicer inserts a color-change command; a compatible printer pauses for a spool change. Check compatibility and plan to be there. See PrusaSlicer's layer-based color-change workflow.
Automatic changes within layers. This is useful when colors share the same height and separating the model would be awkward. It can also save you from waiting beside a printer for planned changes. The trade-off depends on how the system handles filament.
Not all multicolor systems waste material in the same way
In a single-nozzle filament-switching system, the old color must be cleared before the next color is clean. Purging and repeated changes can add material and time. The important variable is often the number of changes, not just the number of colors. Printing several copies together can spread the purge overhead across more finished objects. Prusa's wipe-tower documentation explains this behavior for its MMU workflow.
A tool-changing printer uses separate hotends, so the same assumptions do not apply. Priming may still be needed: Prusa enables a tower by default on the XL, although its documentation describes conditions where it can be disabled. That is not a promise of zero waste on every print. Read the XL guidance.
Compare one real job before buying
Slice the same model in one color and in the intended colors. Keep the printer, material, orientation and quality settings comparable. Record estimated duration, total filament and any separately reported purge or tower material. Then ask whether the colored version saves enough painting, assembly or hands-on time to justify the difference.
Start with compatible colors of one material type. Multicolor is not the same as multi-material: different plastics may bond poorly. Prusa recommends matching material types for color changes.
Our rule: keep single-color printing as the default. Add color where it improves the object—readable labels, distinct features or a finish you would otherwise paint. For a raised two-tone sign, try one planned manual change before buying another machine.