I was recently bought a tube of Smarties. I don't eat chocolate sweets/bars very often and so it must have been at least a few years since I last had any Smarties and I instantly noticed three things 1) the tube was hexagonal and missing the plastic top, 2) the colours all looked washed out and 3) there were no blue Smarties.
Apparently the tube was changed to it's modern form back in 2005 which probably tells you how long it is since I last bought a tube of Smarties!
The colours of the Smarties probably look washed out because at some point the makers, Nestlé, changed the way Smarties were produced to remove artificial colourings and flavours.
There are currently no blue Smarties because there wasn't an alternative natural colouring that could be used.
Having noticed all these things just a few weeks ago I was interested in a BBC news article today that announced the imminent return of blue Smarties. Apparently there is now a natural blue food colouring, extracted from a seaweed called spirulina, that can be used.