Are they Hope mini's?
Things to check:
1. That the rotor bolts are tight.
2. That the caliper mounting bolts are tight.
3. Take the pads out and rub their braking surface on some clean, dry fine sand paper. Then clean the metal backs of the pads and apply a thin smear of grease or Neverseeze to the surface of the metal.
4. Clean the rotor with meths.
5. Take bike to top of a steep road hill (Kirkstone) together with a bike bottle of clean water. Give the pads a good soaking with water and set off down the hill applying the brakes as much as possible. Every 30 secs, stop and put more water on the brakes. This is the fastest way of getting the pads and disks to 'mate' together.
Bluing is where the disk has over heated and a slight 'blue' tinge can be seen on the rotor.
I had a disk that I couldn't stop sqealing on the front of my old Whyte mountainbike until I had the mounts 'faced' by the LBS. But all disks seem to have their squealy moments and as long as the mounting bolts are all tight and the pad free to move slightly in the calipers (crud free with a lightly greased back plates), then sometimes it's just easier to 'ride through it' till it sorts itself out.