PIL的ImageDraw的颜色问题

因为我的图片的单通道的，所以用

draw = ImageDraw.Draw(image)
im_width, im_height = image.size
(left, right, top, bottom) = (info[1], info[2], info[3], info[4])
color=define.STANDARD_COLORS[info[0]%len(define.STANDARD_COLORS)]
draw.line([(left, top), (left, bottom), (right, bottom),(right, top), (left, top)], width=4, fill=color)

的时候，fill的color无论用什么"red"，"green"都是灰色，所以要在

draw = ImageDraw.Draw(image)前面加上一句

image = image.convert('RGB')就可以有各种颜色了