A fluid valve, in particular a return valve for returning residual color, flushing agent, air and/or compressed air from a color line during a color change in a painting system, in particular during loading of a new color during a color change, with a) an opening position in which the fluid valve is at least partially open, in particular for flushing the color line with flushing agent and for loading the color line with new color during the color change, and b) a closing position in which the fluid valve is closed, in particular for applying the new color after the color change, c) wherein the fluid valve is adjustable between the opening position and the closing position, d) wherein the fluid valve switches dependent on the fluid present on the inlet side own medium actuated to the closing position and/or influences the through flow behavior dependent on the fluid present on the inlet side own medium actuated, e) wherein the switching process of the fluid valve is controllable by the viscosity of the fluid present on the inlet side, f) wherein the fluid valve is realized as a membrane valve with an elastic membrane which carries a shut-off body, and g) wherein the shut-off body includes a first conical portion and a second conical portion, wherein a cylindrical portion of the shut-off body is located between the first conical portion and the second conical portion of the shut-off body, and with h) a cylinder, i) a piston which is movable within the cylinder, j) wherein the shut-off body is moved by the piston between the opening position and the closing position, and k) a valve seat, wherein the shut-off body closes the valve seat in the closing position, whereas the shut-off body opens the valve seat in the opening position. a) an opening position in which the fluid valve is at least partially open, in particular for flushing the color line with flushing agent and for loading the color line with new color during the color change, and b) a closing position in which the fluid valve is closed, in particular for applying the new color after the color change, c) wherein the fluid valve is adjustable between the opening position and the closing position, d) wherein the fluid valve switches dependent on the fluid present on the inlet side own medium actuated to the closing position and/or influences the through flow behavior dependent on the fluid present on the inlet side own medium actuated, e) wherein the switching process of the fluid valve is controllable by the viscosity of the fluid present on the inlet side, f) wherein the fluid valve is realized as a membrane valve with an elastic membrane which carries a shut-off body, and g) wherein the shut-off body includes a first conical portion and a second conical portion, wherein a cylindrical portion of the shut-off body is located between the first conical portion and the second conical portion of the shut-off body, and with h) a cylinder, i) a piston which is movable within the cylinder, j) wherein the shut-off body is moved by the piston between the opening position and the closing position, and k) a valve seat, wherein the shut-off body closes the valve seat in the closing position, whereas the shut-off body opens the valve seat in the opening position.