i'ld say it was more likely they didnt keep the original models, after making series 1, then series 2 came along and they had to make em from scratch...you'll never get anything the same if something like that happens, sorry to say!!
btw, end of series 2, with rogg's...well....incident, then the thing right at the end, not gonna spoil it for anyone who hasnt seen it...but this is one of them shows u watch as a kid, then as an adult, and think "this really isnt for kids...why didnt i grow up disturbed?" lol
immaturity and your life is alot like wine, the older it gets, the more it costs you
Drutt was a full on clay model 99% of the time (much like Boni), and they used the same one all the way through both series (I think they got through a few Boni's because he got dirty)
Berk was usually rebuilt from scratch after every few shots, so maybe a change in the original plasticine project may have happened but I'm pretty sure he was the same colour
Berk quit his post as the servant to the thing upstairs at the end of season one. During his absence of almost six months, Berk was living and working in mallorca as a busboy in a top hotel. The suntan he acquired during his working holiday is the cause of his apparent colour change. Nothing sinister at all.
Unless, when they finished the production run of season one, they never expected to make any more episodes, so the threw away the original models, only to have the BBC pick up the tab for another 15 episodes, so they bought some new plasticine for the purpose of replacing the original models?