HI all!i am the OP and I wanted to share how my issue was resolved very swiftly.
i contacted apple through twitter explaining the pink edges problem and my iMac was 8 months out of 3 year warranty . i explained that the product must last a reasonable amount of time by law and that 3.8 years was not reasonable. they suggested i take it into my local authorised apple service centre to start the process.i did this and the very nice guy ran tests on the screen. after 15 mins he said the panel was "bad"
whites and great show pink edges but no other clolurs. thats all i needed to go back to apple and claim that i had a bad panel from day one.
they didn't argue and said they can replace the screen free under 'consumer law' I am in UK btw.they worked really hard to get it booked in same day and then next day it had been replaced ...
very happy with the apple service and really happy with Be Valued apple service centre sussex! they were super fast at fixing it and getting it back to me.
all in all a very happy story

i would suggest anyone with this problem do the same as me and even if its out of warranty, use consumer law which i believe might be up to 6 years after purchase?