To change colors at a specific layer, slice the model, use the slider on the right to go to the correct layer, right click the slider to Add Pause, and change the filament. A more detailed description is here.
At one time this created a layer shift, but I think that has been corrected in recent versions of Studio. If not, Add Custom G-code instead of a pause:
M400 U1 ;pause
G28 X ;home
This is only practical for a color change on an entire layer. I don’t know of a reasonable way to use multiple colors on the same layer without an AMS.