o={0,0}; a={1,0}; b={1,1};
Graphics[{
Red, Line[{o, a}], Line[{b,a+b}],
Green, Line[{o,b}], Line[{a,a+b}]
}]

o={0,0,0}; a={1,0,0}; b={1,1/2,0}; c={1,1,1};
Graphics3D[{Opacity[0.8],
Glow@Red, Polygon[{o,a,a+b,b}], Polygon[{c,c+a,c+a+b,c+b}],
Glow@Green, Polygon[{o,a,a+c,c}], Polygon[{b,b+a,b+a+c,b+c}],
Glow@Blue, Polygon[{o,b,b+c,c}], Polygon[{a,a+b,a+b+c,a+c}]
},Boxed -> False, Lighting -> None]