From SFML source code :
////////////////////////////////////////////////////////////
bool operator ==(const Color& left, const Color& right)
{
return (left.r == right.r) &&
(left.g == right.g) &&
(left.b == right.b) &&
(left.a == right.a);
}
////////////////////////////////////////////////////////////
bool operator !=(const Color& left, const Color& right)
{
return !(left == right);
}
It mean what is write. =p Are you sure you compare the right color, including alpha channel?