I don't know what the procedure is in the UK in regards to late registering of a dog, but you'd need to go through the breeders for that.
That said, as Christina said, your dog is
not a rare color, he is the most common color currently being registered. The exact shade in a blue dog will vary, so the fact that his shade is slightly different from others you've seen is meaningless, and he probably won't reproduce it.
The link you posted to, with his grandsire, is the website of puppy producers, and frankly a poor source of information. One of the points they consider important to mention on your dog's grandsire is that when he's put to blue bitches, all pups produced are blue. Yes, that is what happens. Blue is recessive, blue to blue can only produce blue. There can be varying amounts of white. They note that when bred to a blue and white bitch, the pups had little white, so they assume that Levi has "strong blue". No, he doesn't carry white markings. The amount of white is controlled by different genes than the blue. They note that when bred to black bitches, he can produce blue. Yes, of course he can. If the bitch is carrying the blue trait, when bred to a blue stud, on the average, half the pups she produce will be blue. Nothing special about the stud, it's simple genetics. Other than being blue, the dog has little to recommend him as a stud.
You can talk to the breeders of your dog, and see if you can get registration on him. If you do want to breed him, you need to have the genetic testing done for L2HGA, and hereditary cataracts. You do that through Animal Health Trust:
http://www.aht.org.uk/ The bitch will need to also have had these tests done. The eyes of both parents should also be tested, you can read about that here:
http://www.bva.co.uk/canine_health_schemes/eye_scheme.aspx