Tableau sequential colour scale (continuous)

### ** Examples

dsub <- subset(diamonds, x > 5 & x < 6 & y > 5 & y < 6)
d <- qplot(x, y, data=dsub, colour=z)
d + scale_colour_gradient_tableau('Red', limits=c(3, 4))

d + scale_colour_gradient_tableau('Blue', limits=c(3, 4))

d + scale_colour_gradient_tableau('Green', limits=c(3, 4))