The white-on-blue 1951 tag is notable in two ways. First, it introduced the two letter "county code" still in use today. Second, the tag itself is literally shaped like the state of Kansas — the upper right hand corner is cut, representing the Missouri River.
For 1952, a black-on-white metal "52" tab was affixed onto the 1951 base.
For 1953, the white "52" tab was removed and a black-on-yellow "53" tab was affixed onto the 1951 base.
Kansas returned to all-new tags with the black-on-white 1954 series. This tag is from Barton County
A white-on-black 1955 plate from Sedgwick county. Note the high number :)
The black-on-white 1956 tag returned to the rectangular shape, with a state outline that would continued (with various colors) until the 1980 issue.