I got hold of another copy of the 25mm and the colour cast is identical to the one I have. I can't tell the shots from the two different copies apart. So I'm now pretty sure that the 25mm doesn't match the rest of the set in terms of colour (and it's not just my copy).
Another reviewer found the same issue with the 25mm not matching:
Another flaw to be aware of is that the 50mm flares very easily, but it comes with a lens hood which controls this. This was mentioned in the CVP review and found it the case:
Hope that helps, in case anyone else comes across this thread in the future. Personally, for the price, I'm ok with working around the issues and I'm going to keep the set.