When all the VIBGYOR COLOURS in light medium are mixed ,we get White but when we mix the VIBGYOR COLOURS in paint,why doesn't it result in the colur ,White/?

In the first case, the colours of VIBGYOR pass through a prism,it get refracted, thus the white light is obtained. in the second case, light doesn't gets refracted (due to the absence of any sorts of refractive object rather a prism) the colour white does not appears.