1. How do you keep plasticine models clean? after a while mine get dusty so i was wondering how other model makers do it.

2. Although i have made gromit models before, i can't remember what colours you have to mix to get gromit's colour. does anyone know?

1) I keep my models covered in cling film and this is also what aardman do to keep their models clean.

2) I use newplast clay and they do a colour called 'stone'. Aardman use this colour so if you use is you won't have to mix. here is that colour: http://www.amazon.co.uk/Newplast-500g-Stone-Plasticine-Alternative/dp/B0032BVGD4/ref=sr_1_3?ie=UTF8&qid=1343229251&sr=8-3  

thanks, that really helped i bought Stone and Pink newplast from amazon.

happy to help.  newplast also do a colour called 'flesh pink' which is useful because if you mix it with a bit of white you get the colour of wallace's skin 

1) I use cling film as well. It works GREAT. Aardman uses it, too.

2) Yup, stone will do just fine.

Ok guys here is a plasticine Colours guide for W&G characters - Newplast/Colourclay
  - Pink, White, Dark Brown, Dark Green, Black
  - Stone, Dark Brown, Black
 - Black, White, Pink, Orange, Red
  - Light Brown, Grey, Black, White
  - Pink, White, Light Blue, Dark Green, Dark Brown, Yellow
  - Light Brown, White, Pink, Black, Dark Green

This is only my guess as I have been using a plascitine colour guide to help me determine which colour would suit each character.