On the left is a solution of the permanganate ion, MnO4-, in which manganese exists in the +7 oxidation state. The permanganate ion is highly colored, and as a solid appears nearly black. On the right is a solution of manganese sulfate, in which manganese exists in the +2 oxidation state. In contrast to the permangante ion, the color the the manganese(II) ion is very pale.
(Source: Flickr / igeldard)