Do you think the dark coin has been cleaned and re-toned?
Dale
Hard to judge from a picture, but the reddish discolouring is typical fir Cilit Bang type soapscum :) Then again, what's reddish on my screen may be light green on yours...
Peter
Circulated 1950 and 1951 coins (and 1949) have that characteristic tan colour as seen on the left.
The right hand coins seems to have had a spell in the ground!