begin{tikzpicture} begin{axis}[scatter/classes={
a={mark=square*,blue},%
b={mark=triangle*,red},%
c={mark=o,draw=black}}]
addplot[scatter,only marks,
    scatter src=explicit symbolic]
    coordinates {
        (0.1,0.15)  [a]
        (0.45,0.27) [c]
        (0.02,0.17) [a]
        (0.06,0.1)  [a]
        (0.9,0.5)   [b]
        (0.5,0.3)   [c]
        (0.85,0.52) [b]
        (0.12,0.05) [a]
        (0.73,0.45) [b]
        (0.53,0.25) [c]
        (0.76,0.5)  [b]
        (0.55,0.32) [c]};
end{axis}
end{tikzpicture}