first check for 'op_${opName}' and then for 'op_${ltype}_${rtype}',
as we might want to "{color} != {color}". 

This is not an optimal solution, as a way to override a general operator
by it's arguments type is something good and not viable this way.

The previous fix break the tests and was not good. This is a new one
which just implement the op_neq_color_color method so the "!=" operator will work on colors as well

Implement the op_eq_color_color in order to support the equality between two colors.
In addition, fix small issue on "!=" operator when dealing with alpha value.