why ghost changes the colour of blood stain ??

The Ghost would steal paints from the paint box of Miss Virginia Otis, to replenish the bloodstain on the living room carpet. He explains to Virginia that it is very difficult to get real blood. Moreover, Washington would keep on removing the bloodstain, which made it difficult for the Ghost to continue replenishing it. Hence, he justified his act of stealing paints from Virginia's paint box, because her brother was the one who kept removing the stain. However, once he had exhausted all the red colors, including the vermilion color, he had no options but choose other colors like emerald and blue.