Here's the truth about the blue spots
secure the caliper in a non marking vice and then rotate the plug anti-clockwise like a 'normal bolt'
The surprizing bit here is the fact that the insert rotates inwards after the initial 'break'
....Once the inserts been screwed inwards as far as it'll go, simply push it and the piston out of the rear.
There's only a rubber seal on the insert and thats it
On re-assembly, the insert can only come out as far as the external shoulder on the outer edge of the caliper...presses up against the seal and the jobs sorted
The seals are available in the microfiche of the FJR1300 which has the same calipers
So now you know
FOUND IN A SKIP (thanks for the caliper Cromwelluk :cool )