@Tubby G The first colour graded trails in the UK were all located within the new (at the time) trailcentres. mainly in Scotland and Wales and built in the late 90s when there was more of a split between DH and XC in mountainbiking. Trail centres back then catered to the latter rather than the former and tended to follow forest loops rather than the multiple trails you find now. Of course back then we had plenty DH tracks but none were graded at all. and many locations weren't actually common knowledge outside the DH scene. The original trail centre grading system had a fairly fixed remit.
Blue = easy/beginner. - a smoother and shorter trail route with no real challenging obsticles.
Red = intermediate - medium length with a few more natural features and obsticles but no manditory or unrollable features.
Black = Longer more challenging trails with a more natural feel and some technical trail obsticles.
Glentress was a good example of this... with the original blue trail being a suitable route for families and even kiddy trailers, the Red being faster and more fun with chutes (rollable) jumps and berms. and the Black being a far longer more natural feeling trail with terrain to test your fitness and (XC) skills.
Later on Green and orange graded trails were implemented. Green being properly family/beginner level and Orange being DH/jump/freeride
Fast forward a few years and the trail centre grading system throughout the UK was all over the place with inconsistency.
and now that we have Bike Parks their grading system is completely out of line with the grading system of old.
Personally I've always completely ignored mtb colour grading and just enjoyed the riding regardless whether it's an easy and smooth or gnar to the power of sick.
Llandegla was one of Wales' first trail centres after CYB wasn't it?