Why Has The Damaged Tip Of Finger Turned White After Sticking Plaster Strips?

my sun crushed/cut (badly) his finger tip when a glass coffe table fell on

it had stitches and a bandage for a week and then the hospital removed the bandage and gave us some sticky plaster strips to change every few days.
at first the finger had some colour but now the damaged tip section has turned white which has worried me a bit.

i have read it needs debridation what is this

any ideas