Warning received when using color aesthetic with geom_point

[bobbygs]

Running this code:
ggplot(aes(x='carat', y='price', color='cut'), data=diamonds) + geom_point()

Gives this warning:
'c' argument looks like a single numeric RGB or RGBA sequence, which should be avoided as value-mapping will have precedence in case its length matches with 'x' & 'y'. Please use a 2-D array with a single row if you really want to specify the same RGB or RGBA value for all points.