@Kev101....The change started in the year 2000 as explained in this link taken from The Guardian newspaper dated 2002......
Once, the colour of disability was orange. Orange badges in car windscreens proclaimed the disabled owner's right to parking concessions. Then, two years ago, under a Europe-wide harmonisation, a new parking badge was introduced and its colour was blue. The blue badge was designed to bring uniformity to 12 countries' differing parking schemes.
Not all areas switched over at once however. I think London was later than many in delaying its introduction.